Topic: CB400F Charging Issue

[RickB]

Hi guys,

I've tried to read/search all I can about this so if I've missed a really crucial thread please point it out.

Here's the basic situation. I have a CB400F. After working for months with a mechanic, it's finally running. However it just refuses to charge.

I've got a Dyna S ignition, 5 ohm coils (the black ones), brand new battery, a relay on the kill switch to take the power off the switch.

I've cleaned/polished the terminals at the rectifier.

I tested the three yellow leads at the alternator for resistance. The manual says it should be 0.61 - 0.69 ohms and if higher, replace. I am getting 0.9 ohms, but after reading this post, I understand that my multimeter isn't accurate enough to notice the difference. Still, I've ordered another alternator coil just to be sure.

With the bike off, my battery shows 12.5 volts or so, with ignition on it drops to 11.8 volts or so. At 4000 revs, it's charging maybe .4 of a volt. It's never got above 13 volts. Something's up.

The bike will run fantastic for 10 minutes and as the battery dies, it just gets rougher and rougher until the plugs are fouled and it won't start.

I'm at my wits end. I'm replacing the alternator coil, should I replace the regulator and rectifier also? If there a way I can definitely test both of these units with my multimeter to trouble shoot?

Rick.

[chickenman_26]

Hi guys,
...I'm at my wits end. I'm replacing the alternator coil, should I replace the regulator and rectifier also?

No. You shouldn't replace anything that you haven't confirmed as defective, including the alternator coil.

If there a way I can definitely test both of these units with my multimeter to trouble shoot?

Yes. Absolutely. And it's also possible that all components are good, but you have a bad wiring connection or a wire plugged onto a wrong terminal somewhere. If you want me to walk you through it, PM me. No need to hog bandwidth here.

Stu

[RickB]

Thanks for the words of hope Stu. I've got a good check list for trouble shooting that I found in the FAQ section. That's what lead me to believe my alternator had died. I'll shoot you a PM now with some questions.

I think for starters I'm going to thoroughly go through this check list and see what I can find.

Thanks again.

[Bodi]

The Dyna takes about 10 watts of power for its electronics and it has a very short dwell angle so both coils are on almost all the time, quite a lot more average load than the points system.
The alternator has very little extra power: with a dead stock bike and a healthy charging circuit it's only capable of charging the battery above 3000 RPM or so.
With the Dyna you can't also have a high wattage headlight or extra lighting. If you've put in an H4 headlight with a 50W+ lamp you're in trouble, the battery will never charge. You won't get stranded but you won't be using the electric start. You can get 35/35W bulbs that aren't as bright but still better than the feeble stock headlight.
One easy test is to bypass the regulator. First, fully charge the battery otherwise the test will be meaningless. Then connect the black (BAT) and white (FIELD) wires to the regulator together. These female spade terminals can be slid together to make a temporary connection. Then start the bike with the kickstarter and check battery voltage. Rev to 3000+ RPM for a minute, the voltage should go up to at least 14.5 VDC at the battery.
If not, you have a problem. Either the charging system is not working right or you have too much load. Make sure the wiring harness connections in the alternator foeld and stator coil circuits are really good. In particular there's a set of bullet connectors for the stator coil underneath the left engine cover that cause trouble.

[RickB]

Thanks guys.

I flooded the engine yesterday and couldn't get it started. I left it was the plugs out and charged the battery overnight. I polished up the rectifier terminals. I have yet to test it with a multimeter.

Today I swapped in fresh plugs, put in a replacement starter motor as the old one was shorting out and it started right up. It seems to be missing a cylinder at low RPM's, which makes this alternator problem more pressing.

So I did the tests on the regulator suggested by Stu. It's showing 0.3 ohms resistance, well within spec given the accuracy required to measure that low. I did try adjusting the regulator per the instructions in the Honda shop manual but got no noticeable increase in charging voltage when bending the armature arm.

I then tried testing output on the alternators three yellow wires when revving the bike. Nothing. I may be jumping the gun, but I think it's dead. The three yellow wires are rock hard and one has been broken and soldered back together. To my tests, it just doesn't seem to be outputting any power. I've ordered a second hand part from a wrecker in Sydney. The starter motor he gave me was great, so I've got confidence this will be too.

Rick.

[TwoTired]

electric motors and alternators work, in part, because of magnetism.
Two ways of getting a magnet in an alternator, permanent magnet or an electromagnet.

The SOHC4 uses an electromagnet.

The alternator has a stator (stationary output windings) and field coil (shortened nomenclature for a magnetic field coil).
The field coil is essentially an electromagnet (along with the rotor, which is the metallic core).  Put power into the coil and it creates a magnetic field.  Without a magnetic field, the stator windings can produce no output power.

The Voltage regulator's job is to power the field coil only when the battery is below peak charge.  It uses the black wire to monitor what charge state the battery is in.  When power is needed, it passes all or part of the power received on that black wire, to the white wire, which determines the strength of the electromagnet in the alternator, and thus the power output of the stator.  Of course, the alternator rotor has to spin, as well.

You need to measure the field coil resistance.  S/B about 5 Ω between the White and green wires disconnected from the Vreg.
If you have that, then you need to determine if the Vreg is passing full voltage to the white wire from the black wire.  This is how the alternator is energized.  If both these observations pass, then the yellow wires will have power output (AC not DC, set your meter accordingly).  If you have AC power, then the rectifier should turn it into DC power which can charge the battery.

Unfortunately, it is likely that your "adjustments" to the Vreg have made it work improperly.  So, now it will either shut off the alternator too soon before the battery is fully charged, or once you get the alternator making power is will overcharge the battery and ruin it on long freeway outings.

Hope this helps,

[RickB]

TwoTired,

I was hoping you might chime in. I've read a lot of your posts in other electrical related threads whilst hunting down a solution to my problem and you seem very knowledgeable about the charging systems on these bikes.

Thanks for the break down on the terminology and function of the various components. I'm still very much learning as I go here.

I will have to test the stator with my multimeter in AC mode. I forgot to switch it from DC.

I measured the resistance of the stator by following the procedure given FAQ and it showed 0.9 ohms. Above the specified 0.61-0.69 ohms given in the manual. I have read here that this is a less than 1% variance and given the accuracy of  $25 multimeter, not reliable.

I will double check the regulator tomorrow as you've described.

How do I determine if the Vreg is passing full voltage to the white wire from the black wire?

In your experience, what do you think may be causing me to get no charge at the battery?

My adjustments to the Vreg were very minor. I checked that the gaps where correct with a feeler gauge. They were and I didn't change anything. All I did was bend the armature arm up to see if that increased charge. It didn't, so I bent it back. It may have changed slightly, but given I am getting almost no charge at the battery, I thought it was worth a try. Should I now replace it?

Thanks again for all the help, it's very much appreciated. If I could take this to an auto electrician that knew all this I would. It's terribly difficult finding someone that wants to touch these old bikes.

Rick.

[TwoTired]

I measured the resistance of the stator by following the procedure given FAQ and it showed 0.9 ohms. Above the specified 0.61-0.69 ohms given in the manual. I have read here that this is a less than 1% variance and given the accuracy of  $25 multimeter, not reliable.

Unless the stator has experienced some sort of physical trauma, they very rarely goes bad.  Your testing leaves it the least likely to be the problem, and I would look eleswhere.

The field coil may be another matter, and I am disappointed that you have still omitted that from any testing.

I will double check the regulator tomorrow as you've described.

How do I determine if the Vreg is passing full voltage to the white wire from the black wire?

The vreg closes a contact when the battery requires charging.  So, if the battery V is low, all the voltage measured on the Black wire should be passed to the White wire under those conditions.  The Vreg will reduce the voltage on the white wire (compared to the Black wire) when the battery is above 14.5 V.

In your experience, what do you think may be causing me to get no charge at the battery?

Without actual data reports from you, I can only offer wild speculation.

My adjustments to the Vreg were very minor. I checked that the gaps where correct with a feeler gauge. They were and I didn't change anything. All I did was bend the armature arm up to see if that increased charge. It didn't, so I bent it back. It may have changed slightly, but given I am getting almost no charge at the battery, I thought it was worth a try. Should I now replace it?

Can't say for certain, as I have no test data.  Bending bits inside affect the planned voltage trip points where the vreg takes action.  No one knows where those trip points are, now that you bent up the internals. Are you known to bend things with finite precision?
Will glass break if only hit with a hammer a little bit?  What size is a little hammer to Mr. Universe? 

Anyway, wait to replace it until you get the battery charging and the vreg is the last variable to verify.  You won't be done with the job now until you do the Vreg voltage checks in a mostly working system.  Attacking it before isolating root cause of failure has added to the overall repair workload.
The Vreg's job is to protect the battery from overcharge/overheating when the system is producing the most power that it can, by limiting the maximum voltage the battery receives.  You need to see some charging system power output before making a vreg condemnation, now.  Maybe you didn't change it, maybe you did.  The Vreg adjustments are rather sensitive.  And, I can't see it from here.

Verify physical integrity of the field coil.
Verify the field coil gets power.
Verify the yellow wires deliver power to the rectifier.
Verify the six rectifier diode are operational.
Verify the rectifier connections to the battery.
Then, when the battery is known to be fully peak charged, verify it never gets above 14.5 V @ 5000RPM.

Then you're done.

Cheers,

[RickB]

Ok so I spent all afternoon going through the instructions. Here's my results:



Battery was charged all night. When I took it off the charger it was 13 volts and dropped down to a holding steady 12.7 volts over 5-10 minutes. With the key off it held 12.6 volts. When I switch the key on it held 11.78 volts. I have the headlight disconnected and have the Dyna ignition and 5ohm coils with appropriate relays. Apart from that, the wiring is stock.



The resitance between the white and green wires is 4.5 ohms.





I now tested the stator wires from the harness side of the unpluged rectifier. I had the meter set to AC. The photos above show 0.00 but that's because I don't have three hands. When I revved the engine to 4000 RPM I got these approximate numbers:

1: 19 max, 16 approx holding.
2: 16 max, 13 approx holding.
3: 16 max, 12 approx holding.


The numbers were jumping around so I did my best of figuring what was the highest and what was the average. There were higher values but I tried to be conservative.



Then I 'full field' the field by jumping the black and white wires on the regulator. I then did the above test again.

1: 16 approx holding.
2: 15 approx holding.
3: 15 approx holding.

I also tested resistance between the white regulator wire and the chassis ground. That was 4.6 ohms.

This is a far as I know how to go. Does this provide any insight as to why my battery is not charging?

Thanks again for all the help guys.

Rick.

[chickenman_26]

I would have expected that you would have gotten numbers considerably higher with the alternator full-fielded than with the black and white connected to the regulator. Full-fielded and testing each yellow to ground at 4K rpm, I'd think something around 30VAC would be more appropriate - 60VAC if you tested between pairs of yellow wires rather than yellow to ground. It might go higher if you go to 5K, as that's where max is rated at. Still...  You are getting some output to the rectifier, so check the rectifier.
Questions - With the key on, is the voltage on the black wire = battery voltage? Are you certain the blue jumper wire is making good contact with both wires? Did you test resistance between each yellow wire and ground? There should be no continuity. The meter should read the same as if the probes weren't touching any wires. And what is that aftermarket relay I see? What circuit is it controlling?

Stu

[RickB]

Stu,

I had an auto electrician put the relay on because the Dyna S ignition was sending all that power to the small stop/run/stop switch and sucking too much power. My mechanic thought that issue might have been causing my problems. Nope. The other relay is for the electric start. The stock CB400F push button start was powered, whereas the CB350F switch gear I has an negative powered push button start. If that makes sense. For what it's worth, I had these problems before I had that put on.

As I said, I was conservative with my VAC numbers but I didn't get anything up near 30 VAC. Maybe a flash of a low 20 VAC at most. I'll try again between full fielded yellow wires on the harness side of the rectifier coupler. I will rev to 5000 RPM and make note of the absolute maximum number I see.

The blue wire I used to jump the full fielding was brand new. I will test again with some blade terminals on the wire to be double sure. I'll test the black wire voltage tomorrow and make note of it.

I don't think I have tested the yellow wires to ground for resistance. Only between each other at the harness side of the rectifier coupling. I will do that tomorrow also. To test continuity is this the right setting?



If this is the continuity setting I will test the rectifier tomorrow according to the Honda shop manual.

Thanks again Stu.

Rick.

[TwoTired]

When testing the stator outputs, you measure between each of the yellows.  3 wires, three tests.  These outputs do not need or want a frame ground reference (which is why the numbers were jumping around, you simply confused the meter (and yourself  ) with those probe connections).  The fact that you measured voltage on each yellow lead with reference to frame just tells us that the stator winding are NOT shorted to frame (which is a desirable observation, even if not intended). 

Do test the rectifier with the setting you show on your meter.  Disconnect the rectifier from the bike for the tests.
Their will be 12 tests for the six diodes, each with probes placed in two polarities.  The outcome should be very low readings in one probe polarity and very high readings in the opposite polarity for each of the diodes.

You DO want to know what voltage appears on the Black wire to the Vreg and how it relates to the actual battery voltage.
The knowledge can be gained two ways.  Make two tests; at the battery terminals and the black and green at the Vreg and subtract one for the other.  Alternately, place one voltmeter probe on Battery POS and the other on the Black Vreg terminal (Note reading)
Then, place one voltmeter probe on the battery NEG terminal and the other on the Vreg Green terminal (note reading).  Add these two readings.

Assuming, the rectifier tests good and the stator outputs were 30VAC or higher.  The next thing would be to measure circuit operating voltages.
I would want to see the charge voltage vs RPM readings with the Vreg bypassed (discontinue test immediately if battery readings exceed 15V)

If the battery readings are still dismal.  I would want to see the AC volts on the yellows while they are working or under load.  If the system is simply placing too much load on the alternator, it will prevent the alternator from making the AC voltage peaks needed to transfer power through the rectifier diodes.

A diversion...
You mentioned you have a Dyna -S ignition.  Do you also have 3 ohm coils?  Can you measure the primary resistance of the coils?
I calculated this combination to consume 96 watts (Stock system is 35 watts).  And, the CB400F alternator only makes 156 Watts at an optimum 5000 RPM.
The stock bike with lighting on draws about 120-130 watts which leaves about 20 Watts to recharge the battery @5000rpm.  Since the Dyna-s and 3 ohm coils suck 61 MORE watts than the stock set up, you wind up with a 40 watt deficit that will simply drain the battery to exhaustion.  The situation would be a little better with 5 ohm coils and dyna -s (56 W draw).  But, its only hope restoring the battery is to rev it at 5000 RPM all the time, or to run without a headlight operating.

Maybe you should tell us more detail about ALL the electrical mods you've made to the bike?

Cheers,

[RickB]

Thanks for all the help everyone! I spent some more time testing this morning. Going over everything. Here it is in question and answer format so I don't get lost (and other people may benefit from it later on).

Unplug both the alternator and the rectifier from the bike's wiring harness. Also disconnect the green wire from the regulator. Using your multimeter, check the resistance between the green
wire in each of those couplers, on the harness side of the coupler, to chassis ground. Do the same for the regulator's green wire. There should be close to zero resistance - like less than 1/2 ohm.

The green wire on the harness side of the rectifier to ground tested 1.5, the regulator green wire tested 1.7. Is this bad? Here's a photo so you can verify that I have the tester on the correct setting,



Plug the alternator back in, and reconnect the green wire at the regulator. Make sure the battery has a good charge. You're going to check stator output on the three yellow wires at the harness side of the rectifier coupler. Set your meter to read AC volts. Start the engine, and let it idle while you attach one probe of your meter to ground, and the other to one of the three yellow leads. Watch the meter as you rev the engine to at least 4,000 rpm. Then repeat on the other two yellow wires. What was the maximum AC voltage you saw displayed?

Maximums:
1: 20
2: 21.4
3: 21.7

Next test would be to disconnect the white and black wires from the regulator, jumper them together, and repeat the test. This will "full field" the alternator and force it to put out it's maximum when you rev the motor to around 4,000 rpm.

Maximums:
1: 19
2: 19
3: 19

60VAC if you tested between pairs of yellow wires rather than yellow to ground.

I did get up around 60 on all three.

Questions - With the key on, is the voltage on the black wire = battery voltage?

Black wire= 11.5 volts
Battery = 11.5 volts

Are you certain the blue jumper wire is making good contact with both wires?

Yep, I am.



Did you test resistance between each yellow wire and ground? There should be no continuity. The meter should read the same as if the probes weren't touching any wires.

Yes, it just read 1, which is what it says when nothing is connected to it.

Now for the rectifier. I followed the SOHC/4 FAQ guide (checklist shown below) in both the resistance and continuity settings as I wasn't sure which was correct.

Here is the results on the resistance setting:







Note the 1. I will refer to this as ERROR so as not to confuse myself.

VI.   Check the five leads on the rectifier.
A.   To perform a forward bias test first connect the red tester lead to the green ground lead.
B.   With the black tester lead test all three yellow wires.
C.   Resistance must fall between 5 and 40 ohms.

This showed ERROR, like nothing was connected to the tester for all three wires. See above photo to verify I have the tester set correctly.

D.   To perform a reverse bias test connect the black tester lead to the green ground lead.
E.   With the red tester lead test all three yellow wire.
F.   Resistance must be greater than 2000 ohms.

Same as above, ERROR for all three.

G.   Connect the black tester wire to the red and white rectifier lead.
H.   With the red test lead test all three yellow wires.
I.   All three must have between 5 and 40 ohms.

I got 2.4 on the left terminal then ERROR on the middle and right terminals.

J.   Connect the red test wire to the red and white rectifier lead.
K.   Test all three yellow wires with the black tester lead.
L.   Resistance must be greater than 2000 ohms. 

I got 3.5 on the left terminal then ERROR on the middle and right terminals.

Here is the results on the continuity setting:



VI.   Check the five leads on the rectifier.
A.   To perform a forward bias test first connect the red tester lead to the green ground lead.
B.   With the black tester lead test all three yellow wires.
C.   Resistance must fall between 5 and 40 ohms.

Left terminal: .530
Middle terminal: .578
Right terminal: .543

D.   To perform a reverse bias test connect the black tester lead to the green ground lead.
E.   With the red tester lead test all three yellow wire.
F.   Resistance must be greater than 2000 ohms.

ERROR for all three.

G.   Connect the black tester wire to the red and white rectifier lead.
H.   With the red test lead test all three yellow wires.
I.   All three must have between 5 and 40 ohms.

Left terminal: .001
Middle terminal: .551
Right terminal: .565

J.   Connect the red test wire to the red and white rectifier lead.
K.   Test all three yellow wires with the black tester lead.
L.   Resistance must be greater than 2000 ohms. 

Left terminal: .001
Middle terminal: ERROR
Right terminal: ERROR

Now for TwoTired's suggestions:





You DO want to know what voltage appears on the Black wire to the Vreg and how it relates to the actual battery voltage. Make two tests; at the battery terminals and the black and green at the Vreg and subtract one for the other.

Key in off position:
Voltage at battery terminals: 12
Voltage at black and green on harness side side at regulator: 0
Subtract one from the other: 0

Key in on position:
Voltage at battery terminals: 11.5
Voltage at black and green on harness side side at regulator: 11.5
Subtract one from the other: 0

Alternately, place one voltmeter probe on Battery POS and the other on the Black Vreg terminal. Then, place one voltmeter probe on the battery NEG terminal and the other on the Vreg Green terminal. Add these two readings.

Battery POS and on black at harness side side at regulator: 12.1 (with key in the on position, 11.9)
Battery NEG and on green at harness side side at regulator: 0 (with key in the on position, 0)

You mentioned you have a Dyna -S ignition.  Do you also have 3 ohm coils?  Can you measure the primary resistance of the coils?

I do have a Dyna S ignition but I got the 5ohm coils as I had heard the 3ohms might be a problem on my charging system. My headlight is off unless I turn it on as per the Australian model spec (I believe the US model was always on). I would like to measure the measure the primary resistance of the coils. How do I do that?

Maybe you should tell us more detail about ALL the electrical mods you've made to the bike?

There's the two relays, the lighting in the mini gauges, the CB350F right hand switch and the Dyna ignition with 5ohm coils. Nothing else has been touched and is as stock.

Thanks again for persevering through this for me. I owe you all a beer if this bike runs!

Rick.

[TwoTired]

Looks like a bad diode in the rectifier.  Replace it.

I will add that when you are measuring very low resistances, like 1 ohm, you must subtract the resistance of the meter's own test leads.
Place the probe tips together and note the reading on the display.    Subtract this reading from all measurements made on this meter's scale setting.

Cheers,

If the new rectifier doesn't fix it, it will at least make it better.

Cheers,

[chickenman_26]

Thanks for all the help everyone! I spent some more time testing this morning. Going over everything. Here it is in question and answer format so I don't get lost (and other people may benefit from it later on).
Rick.

You're going back and forth between me by PM and TT on the forum, and you may be getting yourself confused. So I'll ask you to just stay here with TT. You have a bad rectifier. I don't believe your system has any other problems, except possibly a mis-adjusted regulator due to your having bent the spring arm. The rectifier is causing your low charge rate and allowing the battery to discharge partially. When you rev the motor to check the voltage, the charge rate is low and so is the battery state of charge, so it would take 15 minutes of revving before you saw the voltage come up much more, if it ever did. I think if you replace the rectifier with one that tests good and get the battery fully charged, your issues will disappear. TT can walk you through the regulator if that's now an issue.

Stu

[RickB]

Hi guys,

So it was the rectifier!

I tested it for continuity and it only allowed current one way. So it already tested better than the old one. I plugged it in, started the bike, revved it up and it showed 15+ volts at the battery terminals straight away!

Obviously I didn't want to fry the battery so I'm in the middle of stepping down the voltage regulator to match the maximum voltage specs shown in the manual.

Now I'm still dealing with the weak spark (and hence not firing on all cylinders) issue so it's hard to get the bike to idle long enough to really test the max voltage. Anyway, the purpose for this thread, the battery not charging, is solved!

Thanks to Stu Chickenman, TwoTired and everyone else that pitched in. I couldn't have done it without you.

Rick.       

[blight]

Hi guys, lurker here but have made a few posts!
I have had 3 CB400F's from the 70s... still lucky to own two! (Red and Yellow)

Anyway... old RED has had a charging issue for a while, and more importantly, a stranding issue for me over the last few months... it was just dead when turning the key.

I've had to call my wife to come and rescue me twice in the last 6 mos... very intermittent problem and that's why it was so perplexing!

I did all the checking and replacing of batteries (over and undercharged), replaced the regulator, rectifier, even tried the combo-unit... still, the stranding and zero-power issues.

I rode the bike (red) for several weeks with a digital voltmeter taped to the bars so I could keep an eye on the battery voltage while riding... seemed OK for a while.

Yesterday, I rode to fill 'er up at the local 7-11 gas station about 2 miles from my house.... after fueling, turned the key, and NOTHING!
No idiot lights... no neutral light, and no push-button starter action. Yet, the hard-wired digital voltmeter showed 13+ volts! I pushed it sadly over to a vacant parking space. This is a HONDA... c'mon, man!

By the way, I should mention, on the 2 mile ride to gas station, I saw an alarming 16V charge going to the battery!! Alarming, but it got me there.

I had to call my wife (once again) to come and pick me up in my Ford F150... luckily she was home, and picked up the phone to come and get me.

She took me back home, we loaded up my heavy receiver-hitch motorcycle carrier, and went back to haul the dead bike home... great fun for both of us.

Today, I did some 'forensic' electrical exams...I already had a brand new battery, new rectifier, and the original (reliable) regulator.. all checked out!

Perplexed, I did a check of the fuse-box continuity, and while all the glass fuses did not visually appear to be 'blown' , the 15 amp main fuse was showing no continuity!! hmmm....

That is the line to the ignition switch, and sends 12V feedback to the regulator... when it's blown or intermittent contact, the regulator sends full power to the battery, and may fry it!

Additionally, when you turn the key, you may get no idiot lights, and NO electric start... or even kick start.... believe me, I tried. Call yer wife!!

That 15 amp fuse cuts the ignition circuit as well it seems... like 'key-off'

With the continuity check, it was NO-GO!.... popped the fuse out, and just handling it gently, it came apart... the silver end cap pulled right off!

So, to get the bike going again today, I soldered in a modern blade-fuse and connectors to the old fuse clips... even threw in a few spare blade fuses in the tool tray.

I ran the bike afterwards in the driveway, and the charging volts were always over 12V at low 1200 rpm, and never over 13.5V even revved to 5000 rpm... all good!

A (short) test ride will follow tomorrow if it doesn't rain!
BLIGHT

[Bodi]

This a typical tale of a 50 year old motorcycle. The electrical system has some inherent aging problems (just like me...) that will eventually give grief.
Some components are rarely problematic: the alternator coils are one - they are the last place to look for trouble unless visibly damaged: the wire is durable, the lacquer insulation (although it looks fragile) is unaffected by normal engine heat and well protected from physical damage. You can measure coil resistances and confirm no connection to ground but be aware that inexpensive multimeters do not measure low resistances (below 10 Ohms or so) accurately so don't worry if the resistances measured are somewhat "out of spec".
The actual harness wire is not going to just stop conducting unless damaged. The main wrapped harness sections won't be a problem. Where wires go around the steering stem they can degrade from metal fatigue but even after 50 years and a lot of turns they don't usually fail. If the insulation is nicked somehow, the copper will corrode into green mush if water gets there often... inside stored bikes don't really have this problem but any wire nicks should be fixed.
The connections are the number one cause of electrical problems. Those bullet connectors are surprisingly good but they do degrade from corrosion when left undisturbed for decades. Connectors that are unplugged and reconnected even every few years do much better. Going through the entire harness and cleaning every bullet and spade connection's ends resolves many strange electrical problems. You want to look for symptoms of heat in particular: when the clear sleeve over the female end has gone brown the connection has been overheating. A good cleaning of both ends and a gentle squeeze on the female end to tighten the socket and adding a coating of dielectric grease should renovate is to last another 50 years. If the sleeve is burnt black or charred, the connector is not salvageable. This indicates it was very hot... the female socket metal will have been annealed and lost it's springiness, and the wire ends going into the ends will be badly degraded (probably crusty black/green and easily broken off). If the connection is not likely to ever be disconnected you can strip the wires back to good copper then solder the connection and insulate with shrink tube, if you need a connector there you can find replacements online. On the 350/400 the five alternator wires all have somewhat redundant bullet connectors under the engine side cover: these are very prone to failure due to the constant heat cycling with the engine. I recommend cutting those connections out and soldering the wires.
The fuse box is a problem in two ways. First, the fuse clip pieces had a protective/conductive plating when new. After 50 years that plating is long gone and the base metal is prone to corrosion that is not usually visible, and the contact with the fuse is no longer reliable: this causes overheating that makes the contact worse and will melt the solder inside typical glass fuses so that the internal connection is bad although the fuse wire looks perfect. Second, the harness wires to the fuse box are soldered in back (under the removable rear cover) to the fuse clips. Overheating will also melt that solder and the connection becomes intermittent. If they get really hot, the fuse clips melt the plastic case and go loose in it, hot enough and the metal gets annealed. There's no super great quick fix for these problems, the fuse contacts are not fixable. There are available replacement fuse boxes with modern plug in microfuses that have the harness plug and use the original mounting screws... get one.
Switch contacts can go bad but the act of switching cleans the contacts on most switches and except for the plastic bits going brittle or turning to dust they are mostly OK. Except for the start button... the idea of running headlight power through the tiny spring loaded contacts is stupid and they all eventually overheat and melt inside. If yours still works OK, install a bypass relay or just bypass the switch entirely and have the headlight on when starting, it doesn't make any difference.
Battery connections can cause charging problems. There must be a high current very low resistance connection from the battery "-" to the frame and engine. Usually not an issue except after restoration, after painting or powdercoating the frame, the tab where the cable connects must have bare metal exposed to make a good electrical connection. The wire to the fusebox from battery "+" - sometimes from the starter solenoid - should be inspected and the ring terminal cleaned with steel wool or scotchbrite to shiny metal.
If the harness connections are all good after servicing them, your battery is good and fully charged, and you haven't installed aftermarket ignition and/or lighting that increases electrical load above the alternator's designed maximum power output but still have charging problems... then look for issues with the regulator and rectifier. The rectifier is easy to test with pretty much any multimeter. The regulator is not so easy to test for calibration, and adjusting them is far from easy... but a good/bad functional test is super simple. Pull the black and white wires off the alternator terminals, and connect them together. These female spade terminals can just be "mated" by pushing them together, hard to explain but try and you'll get it. Or use a jumper wire. That gives you maximum alternator output: with a fully charged battery and headlight unplugged, battery voltage should go up above 15 volts pretty quickly at 3000RPM. If it does, but you don't see the voltage going up to just over 14V with the regulator connected, the regulator isn't working.