Topic: the most frustrating electrical issue ever

[stockscreamer]

A little run down of what im dealing with in the process of putting new turn signals and taillight on the ole girl ( previous mechanic bought and installed ugly bulky black ones  and an ugly "dune buggy or trailer light for the tail ) ive run into the issues of 1. Bike will turn over no matter the RH kill switch orientation on/ off. ( also dont know if its related to this same issue or if its another entirely is the right side coil was getting warmer the more that i was probing around with the multimeter) 2. Headlight and tailight does not come on when the ignition switch is turned on only when i turn the tach and speedo lights on does the headlight and taillight come on.. not sure if thats normal or not because apparently from previous posts ive seen i have the most bastardized honda of them all electrically  75 k5. I have already done uber google searchs nothing really relating to my issues.. the nuetral light also has went out recently ish didnt really think it was related though.. not popping fuses everything seems to be wired correctly.. im stumped i thought i had it narrowed down to a short from the wires coming from black/white and and yellow and red.. i imagine they had been heated pretty good insulated was still in tact better not good i could get it to leak about 10.5 volts touching insulations together.. everythings all back together with new wires and still does the same stuff. Any help would be greatly appreciated.
Sorry its been so long since ive been around but the ole girl does very well usually not needing any questioning. Also another thing may or may not be an issue. The start motor safety unit gets warm when the ignition key is on just sitting there .

[seanbarney41]

Starter will work regardless of kill switch position...that's normal.  The kill switch only switches power to the ignition...Are you saying you have a switch for your tach and speedo lights?  That's not normal, and if so, there has been some previous owner wiring hijincks going on.  You need to download a wiring diagram and learn how to use it.  Otherwise it is very difficult for us to help you. 

[stockscreamer]

Ive went through 3 wiring diagrams that were wrong even though they were marked as my year..found one that actually has all the options my k5 has
left hand switch controls hi/low beam, turn signals and horn all work as they should except hi-beam switch stuck on hi beam.. right hand switch has the emergency kill switch, an on/off switch that turns on taillight, headlight, speedo and tach lights  and then the starter button. Previous mechanic installed big black bulky cheapo 3 wire turn signals all around hes drunk more than sober so i undid everything he did and put the new 2 wires on.. 
All my wires are going where they should be up in the bucket and only have the one solid brown empty connector that all us models have..

[calj737]

As Sean said, your gauge lights and tail light are NOT wired per stock. They come on when the key is switched on. The KILL switch only interrupts power to the ignition.

You seem to indicate that the wiring to the coils is new but still shows a voltage of 10.5v? That's a pretty good indication of a problem at the handlebar switch. Sounds like it's time to open the handlebar switches up and correct/restore the wiring and remove any corrosion you might find there.

[mystic_1]

Looks to me like the K5 has a switch on the right hand control that turns all the lights on.  Terminals IG/TL1 on the "Headlight Control * Emergency * Starter Switch" control at the top of the diagram below. Black wire brings +12V to the switch, output Brn/White wire feeds power to all the lighting circuits.  So, this sounds normal to me.

The "Emergency" switch feeds power to the coils via the Blk/White wire.  Has nothing to do with the starter.  Again, normal.  Bike should crank but not start with this switch off.

You mentioned that the right hand coil was getting warm during testing.  I'm betting that the bike was not running and the points for that coil were in the closed position, so power was being fed to the coil continuously.  This again sounds normal, although I expect the power would have to be on for a while before the coil heated up noticeably.  If it heated up quickly, I'd suspect a possible bad coil, check the resistance on the primary and secondary windings to check for this.

You mentioned that the starter motor safety unit gets warm, I don't have any experience with these (K0 here) but I see that the safety unit drives the neutral light on this bike, so it wouldn't surprise me if you have a bad safety unit and that's why your neutral light no longer works.  You mentioned the Yellow/Red wire looked like it had been heated/melted so that would seem to support this theory.

To test this, disconnect the yellow/red where it comes from the neutral bulb and ground it (with the key on).  If the light comes on, this would seem to suggest the problem is with the starter safety unit.

mystic_1

[stockscreamer]

Calj- ive replaced the wires from RH switch to the headlight bucket.. bc voltage was leaking THROUGH wire insulation  inside the switch assembly and a little bit past where the assembly comes together on the handlebars.
mystic- i was fiddling with her for a good 45 minutes before i noticed it was warm not hot just warm enough to notice so i think im good on the coils as well. Im not home right now but i will check into the starter safety unit asap and come back with what i have found.. thank you for clearing the switch up for me as i have seen countless threads about 74-76 having a ton of different configurations when it comes to lights coming on automatically and such.. thanks for the leads : )

[Grinnin]

1. Bike will turn over no matter the RH kill switch orientation on/ off.

Normal as others have mentioned.  As long as it won't start.

2. Headlight and tailight does not come on when the ignition switch is turned on only when i turn the tach and speedo lights

My 750K5 is the same.  The rocker switch on the right switch pod turns on the headlight, front marker lights, and instrument illumination all at the same time.  Only the taillight comes on with the ignition.  This agrees with the 2 wiring diagrams that I have.  Others have said that your bike acts wrong here and I disagree.

3. the nuetral light also has went out recently ish didnt really think it was related though

The neutral light should not change how the motorcycle works.  It would change how I work, though.

4. not popping fuses everything seems to be wired correctly

Good.

5.i could get it to leak about 10.5 volts touching insulations together.

Not so good.  Your response, to replace the wires, is good.

6. all back together with new wires and still does the same stuff.

Points 1 through 4 are all normal.  5 is not, but I hope you've corrected it.

7. The start motor safety unit gets warm when the ignition key is on just sitting there .

The Starter Motor Safety unit includes a couple diodes, a PNP transistor, and an NPN transistor. The diagrams I've seen and the reading I've done all show a light bulb inside that black box (OK, grey box on mine).   I believe the diagram is wrong and the light bulb shown as being inside the SMSU is actually the dashboard neutral light.  The case on my SMSU is so cracked that I'm replacing it with a single diode.  This change will pass all the current for the starter solenoid through the starter switch and either the neutral switch or cluth switch.  That's about 3 amps, which should not be any problem at all.  Honda changed to a single diode a couple years after my '75.  The ONLY reason that I can see for the circuit in the SMSU is to use small currents at the switches and provide a larger current to the starter solenoid.  This could be my blind spot, but a single diode will work. .  You don't need to push any buttons,

YOU'VE DESCRIBED SOME ODDITIES.  The insulation is a real problem.  The neutral light may be a bulb or a switch, but easy enough to find and correct.

Is there another "problem" that I didn't find in your description?  Is there a problem with the turn signals?  Note that the K5 has single-filament rear signals -- they're on only to indicate turns.  It has dual-filament front bulbs -- they are "running" lights when the turn signals are off but when you turn on a turn signal, the other filament turns off so the flash is more visible.

[lucky]

Get rid of the starter motor safety switch.
Almost all of them are warped and cracked from excessive heat trapped inside of them.
The heat sink is inside the case! No cooling air can get to it.

Do a search on this site, and jumper wire the female plug that the safety switch plugs into.
Just one wire jumper.

[oldhatt45]

stockscreamer,

What the rest of the guys have said are all valid points.
What I'm going to suggest is what I would do if faced with your situation.
It will not be a quick fix and will involve a fair amount of time to do right.

Get a LARGE piece of paper (at least 24 X 18 inches).  Get a box of colored pencils.
Layout the closest wiring diagram next to your blank sheet of paper.
Start by putting the various components on the large paper in the approximate places on the reference diagram.
Leave plenty of space around each component for notes, etc.
Then go to the bike and physically start filling in the wiring between components using the appropriate color pencil.
Add notes for each wire, such as voltage on that particular wire, if warm, hot, etc. under what condition such as; key on, key off, running, not running, etc.  voltage when wire a is touched to wire b.  Also parts names/numbers.
Once you have all wires accounted for, you should by then know exactly what is happening under what condition and should be able to easily determine what and where the problem is.  Your new diagram will also be a good reference if you ever have any future problems.

I know there are some that will think that my suggestion might be overkill, but it's the only way I can think of to make sure you have everything straight and accounted for and can easily troubleshoot the entire electrical system on your bike.

Hope this helps.

Charlie

[70CB750]

Get rid of the starter motor safety switch.
Almost all of them are warped and cracked from excessive heat trapped inside of them.
The heat sink is inside the case! No cooling air can get to it.

Do a search on this site, and jumper wire the female plug that the safety switch plugs into.
Just one wire jumper.

+1

[stockscreamer]

1.Gas tank and side covers are off getting painted and airbrushed so i cant confirm that the kill switch prevents it from running but the wires are new with new solid solders (never tried starting it with the kill switch on til this issue lol)
2. Heres where it gets a little fishy tailight doesnt come on until the light switch is flipped on.. works as a brake light as it should.
Turn signals all work how i want them to as purely turn signals no running lights.
  Still at the shop working until further notice so i dont have anything new.. buuut i do have a question, if said starter safety unit is bunk and i make the jumper wire deal are there going any adverse consequences like neutral lights not working since thats where power for it comes from? I really dont want to spend the pretty penny im sure they are asking for a new one (who does)  any real solutions or fixes?

[stockscreamer]

Just tried grounding the Green/red wire from the neutral light with no avail checked the black wire feeding it and its pushing 12, so the bulb must burned out. Would it be dumb to assume that the starter motor safety unit caused the bulb failure? Like you said about the red/yellow wire there has to be SOMTHING that cause the excessive heat in the wires..
Just another thought/question if my SMSU was crapping out wouldnt i have starting and running issues? With all the electrical issues weve had ive never had an issue starting or running it (omitting the main fuse blowing ovbvously but i havent had a fuse blow in years since ive installed blade style fuses)


Update: left the key on only no lights or anything and it seems the smsu is definatley getting warm its been about 10 15 minutes on now and the heat seems to be coming from one side of the unit the side closest to the black wire entering it (not sure if thats really relevant because idk where the wires lead to inside the actual box just trying to be thorough.

I still dont see how all this can add up to my tailight not coming on with the key like it should as thats my only complaint with her right now besides smsu heating up which i wouldnt think is normal. Now that i think about the high beam and neutral indicator bulbs are blown but there older than i am i bet so thats to almost be expected.

[mystic_1]

I can't see how the safety unit could cause the bulb to go bad, so I wouldn't worry about that if you simply find that the bulb is burned out, replace the bulb and if it burns out again then you'll know you have a deeper problem.

BTW here's that circuit diagram of the starter safety unit that Grinnin mentioned, and as lucky said, these are known to fail so it can't be completely ruled out.

mystic_1

[DH]

Does the engine crank when the button is pressed? or does the engine crank, but not run? I'm a little confused, as in your first post you mentioned the engine"turned over no problem". To me, that means it cranks with the starter. Just clarifying....

[Patrick]

You can wire around that safety unit by running any key-switched hot wire to the solenoid. The starter button on a K5 works by grounding the starter circuit. The safety unit allows the bike to supply the positive charge to the solenoid only when the clutch is engaged or the bike is in neutral. Supplying an alternate hot wire lets the solenoid start the bike regardless. It also shouldn't affect how anything else works.

[stockscreamer]

DH- engine will turn over with starter button, last time i tried it started right up.. like i said i cant verify that it will run right now but it gets spark when coils are hooked up ( have them unhooked while searching for these gremlins ).
Pat- i d really like to keep it how it should be and neutral light workng when it should and stuff because im not the only rider on the bike. So i guess my next question should be would the smsu fail all on its own due to age or does a connection or issue down the line cause the failure. Thats one reason i dont want to do away with it because if its somthing further down the line im sure it will show its true colors on a long trip down the road.

[mystic_1]

Well....

http://www.ebay.com/itm/like/231455075958?lpid=82&chn=ps

$17 Buy It Now

I see a few more listed as bidding auctions right now on eBay starting at $5

Spares don't hurt.  I doubt Honda still sells them.

mystic_1

[stockscreamer]

I just bought it up lol good eye. Mine resembles this one in no shape or form lol. Both mounts are broke off the plastic case is cooked.. hopefully this new to me ones better

Is it possible i have a bastard cb750 that was wired to not have the tailight come on with key switch?? Lol no matter what i do i cannot get everything to function together happily unless i have it wired the way it sits now.
PO/current other rider always had the light switch on so no hint there really.. and i really dont see the smsu being the issue with the taillight at all.

[Airborne 82nd]

Gas tank and side covers are off getting painted and airbrushed so i cant confirm that the kill switch prevents it from running
I'm lost what does this have any to do with you testing??

like i said i cant verify that it will run right now but
Again you don't need the side covers or the bikes tank. I must be missing something
Can you tell why you need those things? You can make something like this out of a old law mower gas tank.
http://www.jpcycles.com/motorcycle-auxiliary-gas-tanks?utm_source=bing&utm_medium=cpc&utm_term=aux%20gas%20tank%20motorcycle&utm_campaign=gas+tanks%2C+caps+and+accessories&cid=MSN+SEARCH+NON-BRAND+Category+-+Gas+Tanks%2C+Caps+%26+Accessories&creative=3851840500&device=c&matchtype=b
I don't know what the side cover have to do with it

[stockscreamer]

The fuel tank holds well fuel so that is needed to run.. like i said several times though i have no doubts of it running it gets spark and has never let me down in that aspect ever. The problem lies with the taillight and probably the smsu (mine was worse for wear and heats up with just the key being on). Sorry for the misunderstanding but thorough reading of my posts will clear it up. The only reason i brought up side covers is because they are off to get painted together with the gas tank...

[Spanner 1]

This thread is a classic example of why I don't hardly post any replies to 'problems' anymore...

[stockscreamer]

This thread is a classic example of why I don't hardly post any replies to 'problems' anymore...

care to elaborate?  I believe that i described my problems clearly, have gotten a few helpful posts from fellow members (thank you all). Not trying to offend anyone by any means if im slacking let me know im all for constructive critisism.

[oldhatt45]

stockscreamer,

I'm not trying to be a smarta*&^, or offend you or anyone else, but from where I sit, you have a bike that has had "modifications" done to the wiring.  That much seems apparent from your description. 

Several members, have given you "point" solutions that may or may not work, but you still don't know the root cause of your problem.  It almost seems like you are looking for the "magic bullet", but it isn't happening, so you need to fall back and go through some logical sequence to figure out the problem and get to the solution.  Until then, the information that everyone is giving you may be relevant or it might not.  If someone suggests something and it works, great, but you don't have the kind of problem in my opinion that will be a "book" answer.  You will ultimately need to do some work that will take time and effort, but will give you a better understanding of your bike. 

Sorry if I have sounded like I'm preaching, but sometimes you just have to bite the bullet and do something you don't want to do to get to where you want to be.  Feel free to ignore this or understand that I'm really trying to help.

Charlie

[Grinnin]

BTW here's that circuit diagram of the starter safety unit that Grinnin mentioned, and as lucky said, these are known to fail so it can't be completely ruled out.

mystic_1

I believe the diagram is wrong.  Specifically, the diagram shows a light bulb in the center of the SMSU.  I believe this is the neutral light at the handlebars.

The diagram shows that the light bulb is connected to the "main switch" and the neutral light (light-green w/red).  There should be a straight circuit through the SMSU with only a lightbulb (i.e. only resistance).  No such circuit exists.

WRONG:

WRONG.

The black wire from the main switch looks like it's connected only to the yellow/red wire and connected only with a diode.  There is no path from the main switch (4) to the neutral switch ( 8 ) that has only resistance (light bulb).  This is consistent with the SMSU having no lightbulb where the diagram shows it.

Full-bike wiring diagrams show power from the main switch branching to the handlebar neutral light then branching again to both the SMSU and ground.   This is consistent with the SMSU having no lightbulb where the diagram shows it.  It is also consistent with that light bulb being the handlebar neutral light.

In short, I believe the diagram in Honda's CB750 manual is incorrect.

The source of heat inside the SMSU box is most likely the larger of the two transistors, the one with the heat sink.  The heat sink in a small sealed plastic box.

EDIT:  WTF??  I tried to mention diagram items four  (4) and eight ( and I get a smiley instead.

[mystic_1]

Is it possible i have a bastard cb750 that was wired to not have the tailight come on with key switch??
...
and i really dont see the smsu being the issue with the taillight at all.

I agree I don't think the SMSU has anything to do with the taillight, glad to hear you scored a spare!

Re: the taillight, I'm beginning to suspect that what you have is normal for your bike.  I'd have to trace through the diagram more to be sure, but it looks as if your key switch TL1 receives it's power via the BRN/WHITE circuit, which in your bike is switched at the headlight control switch on the right side (which gets its power from black).

TL1 is switched to TL2 when the key is on, TL2 feeds the brake light.  SO, your behavior seems to be normal for this layout.

Another test:  put your key into the second position (P) = you should get taillight only, nothing else.  (Parking mode)

mystic_1