Topic: Need help tracing wiring from begining to end

[JWB]

When I bought my 74 550 project bike it was missing most of the main and sub wiring harnesses in addition to a few electrical components like the starter solenoid, coils, ignition switch and fuse box.  I have reassembled everything with new or used parts using the information on this site and an original wiring diagram.  Even though all the wire colors seem to match up correctly, it is not surprising to me, nothing works, no power to anything.  I am looking for some advice on how to trace\troubleshoot the electrical system starting from the beginning, which I assume is the battery, to the end.  Does anybody have information or a check list on how to accomplish this.  Any and all suggestions are appreciated.

[Kenzo1979]

First place to start is the battery. Is it good and fully charged? If so, is it properly grounded to the frame? Bare metal on the frame? Not painted or powder coated part of the frame. Is your main fuse good?  After that your positive lead is going to go to the main fuse and also to the solenoid, but don’t worry about the solenoid right now. After the main fuse it should go to the ignition key switch. And then from there, the key switch will connect battery positive to ignition positive, the black wires. So the first thing you need to trace is DC volts at the battery, keeping your negative meter lead on the ground, Go to wear red enters the main fuse, then check the other side of the fuse, then you could check it at the 4 pin connector for the ignition switch.  Start there.

[Tracksnblades1]

Start at battery.
+pos  -neg = +12volts.
Check both cables…
Check voltage @ fuse box

What have you checked so far?

Isolate circuits. Check one at a time.

[JWB]

New fully charged battery.  Clean metal between battery and harness ground as per SohRon's excellent 550 assembly manual. Positive battery cable to one side of the solenoid along with large(red) positive lead from main harness. The other side of the solenoid goes to the starter.  12v across two poles of the starter solenoid. No voltage at the fuse box with the ignition key off or on.  That is how far I have gotten so far.

[Bodi]

Hopefully you have a Honda wiring diagram for your exact model and year. Little things changed over the years, probably nothing major but it's best to have the right diagram. Other wiring diagrams - Haynes, Chilton, weird ones on the web... useless or worse. They simplify the system and that just confuses.
First, you need +12V battery power on the MAIN fuse. This connects directly to the battery + terminal (or to the solenoid post the fat battery + cable goes to) via a red wire that should have a red fibreglass sheath on it (I think it's the only wire with the sheath, if this unfused one wears and touches metal you probably have a fire).
Start with the fusebox and the wiring to it. Find out why it doesn't have power. Open the back of the fusebox (pries off) and measure at the red wire, it's not unusual for the fuse to have heated up enough to melt the solder where the wire connects and the resulting bad connection to destroy the wire so there's no contact. Check the plug wiring too, those contacts can corrode and fail as well.
I think the lack of power to the fusebox is your biggest problem. Everything on the bike gets powered through the MAIN fuse - other than that fuse only the alternator rectifier output connects directly to battery + without a fuse.
Once you have power into and out of the MAIN fuse you can trace each circuit either with a meter or test light. Just have the kill switch OFF during testing, you can burn out a coil by having it powered for a long time with engine off.

[JWB]

I have a copy of the wiring diagram out of the owners manual for a 74 550, so hope that should be the correct one.  When you say the MAIN fuse, I assume you are talking about the fuse box pictured below.  The only sheathed red wire that has a round connector that fits over the positive post of the solenoid comes from the main wiring harness.  From the looks of the size and color of the fuse box wires it appears that there should be a feed, but not  sure how to tell if that same red wire goes to directly to the fuse box unless I start cutting the harness apart. 

[Kenzo1979]

Yes on that fuse block, you should have three fuses, one is 15 amp, another is 8A and the other is 5A.  The 15A is the Main (red).  Unless your fuses are in the wrong place. Put your meter to ohms or tone test. Put one lead on the solenoid connection from battery positive and touch the fuses On each side. You should get a short or beep when you get continuity meaning you are touching the same connection. That will tell you where that red wire is going if you can’t see it.

[JWB]

Got it now.  I wasn't testing the fuse block correctly, but only getting power to the 5amp fuse.  Nothing on the Main, 15amp fuse.   
Additionally, I energized the solenoid manually by jumping it directly to the battery, and the starter kicks in and turns over the engine just fine.
Am I on the right track, or jumping ahead too far?

[bryanj]

Have you got the red ring terminal on the solenoid lead from the battery?
Check the voltage on the back of the fuse box as fuse clips are notoriously dodgy

[Kenzo1979]

If you’re getting voltage at the 5A, you would be getting it at the 15A, because the main fuse feeds the key switch that gives power to the other 2 fuses, Brown (Tail light) and Brown/White or Brown/Red (headLight) - ‘74 was Brown White I believe.  when the key switches in the on position, it connects red to brown feeding fuse, brown white feeding fuse and black ignition positive to all of the blacks feeding 12 V — headlight bucket , the coils,  rear brake switch, etc.etc. and everything else that has a black wire connection.  Just think of black as an extension of red When the key is turned on. 

[JWB]

Yes, the positive cable from the battery is connected to the same solenoid post that the red sheathed main harness wire is.
Question: Is the voltage throughout the electrical system 12v?  I know it is 12v at the battery, but want to make sure I am testing correctly as I start tracing wires and checking voltage.

[Kenzo1979]

Yes.  Everything works off 12VDC.  In fact, you can test many things by putting them straight to a 12V battery, just get the polarity right when dealing with DC.  Wondering if your light works?..just connect center pin to + and shield/base to -  .  Horn?..black to + and Light Green to -  .

[Tracksnblades1]

JWB,

If I were you. I would determine why you have no +12 volts at the 15amp Main fuse. And what is causing it.
Very little will work until your “Main” circuit becomes energized….

[Little_Phil]

The thick battery +ve is connected to the starter solenoid and as Bryan has pointed out there are additional connections at that SAME point.  A red (usually with extra sheath) that goes directly to the 15A main fuse plus a r/w that splits off somewhere and goes to the rectifier. Connect meter between bike earth (-ve) and the fuse and you should read 12V at both sides of this fuse. If only one side of fuse, the fuse is blown or the fuse clips are dodgy. From here I think another red goes to the ignition switch. After this many +ves are black.

[MauiK3]

Should the main ground wire go to a bracket or should it be on the frame? Not familiar with 550's.

[Kenzo1979]

It’s on one of the engine mount bolts to the frame a little under the battery box on the right hand side If memory serves me correct.

[Bodi]

Your ground cable frame/engine connection is correct, and if the starter cranks when you jump the solenoid studs then the battery connections are good.
It's that sheathed red wire that goes from the solenoid to the MAIN fuse. Open the back of the fuse box and make sure it's securely connected to the fuse clamp. If it is, there has to be a break in that red sheathed wire somewhere: except for possibly a tee connection with the rectifier red wire, it goes directly from the solenoid stud to the MAIN fuse.
Once you get that figured out, the other end of the MAIN fuse goes directly and only to the key switch. Then the bike should power up when you switch the key on, with power on both the HEAD and TAIL fuses (maybe not if you have a headlight switch in the switchpod). Note that the "P" or park key position changes the tail light wiring a lot, so don't worry about that for now.

[bryanj]

Go back to basics,
Put the neg meter lead on neg of battery securely
Using pos of meter check volts at
Batt
Solenoid
Input of fuse
Output of fuse
Ign switch in
Ign switch out, with key on,lights off and kill switch off

You should get same voltage at every point with a max volt drop of 0.5 volt by time you get to ign out

[JWB]

Went back and cleaned all the connections on each side of the block connector for the fuse box and now I am getting the correct voltage at the main fuse.  With that done, I am making progress one light\switch at a time.  Slow but it is progressing.
Thanks everyone for your help.

[JWB]

Wiring is all complete and everything works properly except the starter button.  When I press the start button all the lights\gauges etc. dim just a bit, but the solenoid does not engage.  I checked the starter button, clutch switch and emergency shut off for continuity to make sure they were working correctly when pushed\engaged.  I also engaged the solenoid manually and it works just fine.  On the solenoid, one top post is connected to the battery, the other to the starter. The two wires, r/y and g/y are connected as per the diagram.  The 2 wires that engage the solenoid, the r\y is connected to the r\y on the starter button and the other which is supposed to be black and connected to the black on the voltage regulator is connected as per the diagram also.
Any ideas?

[Alan F.]

Sounds as if there's still a start switch issue or an iffy ground.

I'd disconnect the battery and start button from the headlight bucket wiring and put an ohm meter across the start button wires first. The switch shouldn't have much resistance at all.

[JWB]

I traded a bunch of messages with Alan and he helped me eliminate some possible issues, but still no luck at this point.  I may try bypassing the SSM at this point.  No danger at this point since the bike isn't running yet.  Wanted to get the wiring correct before I put gas in it and try to get it running.
Here are the messages Alan and I traded.

Alan,
Do I need to disconnect all the black wires from the bucket?

John,
Disconnecting the battery is just a safety measure and you'd only need to disconnect it at the positive terminal.

An Ohm meter if you're unfamiliar measures resistance by supplying its own voltage and essentially subtracting the voltage drop through a resistive circuit.

Anyway I'd recommend you disconnect the start button from the headlight bucket and measure it's resistance. Leaving it connected and measuring it will not give you a true reading of the switch because everything else connected will affect the measurement.

I'm not familiar with which type of start switch your bike has, some have 2 wires that connect to the headlight bucket, some have 1 wire that connects in the headlight bucket and the other contact is connected to the handlebars which are grounded by another wire into the headlight bucket, an there's a third kind of switch that has a few wires coming from it so that when pushed it can turn off the headlight and then turn on the starter solenoid. These are the most complicated and it sounds like that's what you have. These switches can fall apart and fail over time, some can be cleaned up but there are a bunch of small parts inside that can easily be dropped and go missing so be very careful if you need to work on your switch.

I'd recommend spraying some electrical contact cleaner into your start button switch, it'll clean the contacts and lubricate the moving parts.

Alan,
I got 5ohm resistance at the bucket then traced the wires back down to the electrical panel and finally disconnected the SSM and found that is was the source.

John,

Ok, good then your issue isn't at the starter button.
Is there any resistance when measuring the wires to the starter solenoid?


Alan,
All ok on the solenoid,

John,
So I guess you've got a sticky starter solenoid then. Is it the original? After years of use they can get dirty inside and bind just a little, also the contacts can become dull and pitted. There are threads about disassembling and cleaning them up, no need to replace it.
I'm not sure if the starter motor safety unit should or should not have a 5 ohm resistance, but it's not all that much and I wouldn't worry about it much. I'm sure someone else could advise better on that.

Alan,
The solenoid is new.  I am going to try another one that I got in a box of parts when I bought the bike.

John,
Sounds like a plan.

Logic check if I'm understanding correctly:
1. You press start and lights all dim but no crank-over.
2. You short the solenoid posts and get crank-over.
With just the small wires of the solenoid connected, you should be able to press start and hear it click.

Alan,
The different solenoid didn't make any difference.  No click when the start button is pressed, just the dimming of the lights.
I wonder if the black terminal on the voltage regulator is the correct place to connect the g/r wire.  There was no such wire on the sub-harness so I made my own connection to match what the wiring diagram indicates.  Just for kicks I tried the green and white voltage regulator instead of the black.  When using the green the starter engages as soon as i turn the ignition key on, when using the white the starter engages when I depress the clutch lever and disengages when I press the start button while holding the clutch in.  Not sure if any or this information is helpful or confusing.   
Is there a way to bypass the SSM? 

John,
Hmmm. There is a way to bypass the safety unit, I remember reading a thread that said afterward it would work like a K0-K2 where you can bump the starter in gear with the clutch engaged...so be careful.
Have a look at this: http://forums.sohc4.net/index.php/topic,143626.msg1632523.html#msg1632523
I don't know where to go next, but I guess you've ruled out a few more things.

[Alan F.]

And if you put your DC volt meter leads one on each of the starter solenoid's small wires and (with clutch held in or transmission in neutral or both) press the start button...

Is any voltage measured?

[JWB]

Yes, about 2 volts.  I must have held down the start button a bit too long as I blew the main fuse.  Time to run out and get some new ones tomorrow.
Thanks for all your help so far.

[Alan F.]

You're welcome, I'm no expert but I do know a thing or two.

2 volts isn't enough to pick (activate a relay) the solenoid, that's the circuit where your problem is. There's a high resistance condition in that circuit high enough to blow the fuse. This high resistance could be a dirty or corroded connector, ground or switch contact. Also the contacts in your fueebox could be at issue. Looking for something that warms up more than you think it should might reveal the issue.