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Discussion Starter #1 (Edited)
I just got a 79 CX500 Deluxe and have been going through cleaning things up and trying to make it all work right. Eventually will do a lot more, but want to make it all runnable first.

The headlight does not work at the moment. I am not 100% sure what voltages should be coming through.

I have checked the headlight to make sure it works when wired directly to the battery (not sure if that's a bad thing to do) and replaced fuses under the key. I created a new ground and got it to kick on for a quick second and then nothing again. Have jiggled all wires and ran my hands around as much as I could to check for anything loose, but am stumped.

Anyone got an ideas? Turn signals work, gauge lights work, and dummy lights come on too.
 

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Discussion Starter #3
My apologies, was in a hurry at work to get something sent. Updated some info now.

I do have a multi meter. The more I read, the more I think that I am shooting for 7 volts on the prongs?

I've got double blue, double green, and single white I believe.
 

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Have you obtained a copy of your bikes wiring diagram, essential when working on the wiring.
 

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Discussion Starter #6
Have you obtained a copy of your bikes wiring diagram, essential when working on the wiring.
I found an image someone else on here had shared for the wiring, which has been a huge help to me here. I am starting to believe there is a weird short somewhere in the ground. Not sure how, but I ran a jumper wire to the ground (again) and randomly turned the key on to see my headlight shining. I'm going to go through wires again and see if I can make it short out to trace it back to the bad one if possible. Otherwise I guess I will find a new ground for it.

Thanks for the help! If this doesn't work, I'll be back with more questions.
 

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The headlight worked when wired direct to the battery? If so, then the ground circuit to the headlamp is working properly. Your problem is likely in the ignition switch or the start button or the wires connecting those parts. Begin to trace from the battery to the ignition switch to the start button to the high/low beam switch and the headlamp. Check for voltage at those points. Look for an open circuit.
 

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Do you have the correct wiring diagram for your bike? It will say "1979-1981 CX500 Custom & Deluxe" (there are differences between models and years) If not you can find the right one at the CX Wiki (links in my signature and reclinedrelic's). It is also recommended to download the appropriate Factory Shop Manual for your bike while you are there.

Testing the headlight bulb was exactly the correct first step. If you did that by connecting a jumper from the battery + while leaving the bulb connected to ground through the bike's wiring your ground circuit is OK. If you connected both terminals of the bulb to the battery maybe not.

If the other lights are working the ignition keyswitch is not likely to be the culprit because none of its contacts switch just the headlight. The Start button has 2 sets of contacts, 1 to send power to the solenoid and the other to turn the headlight off while the starter motor is operating and it is quite common for the contacts that turn the headlight off to become dirty and prevent the light from turning on when the button is released.

The fix is easy: Clean the contacts. Get some real electrical contact cleaner (NOT WD40 or anything else that will leave an oily residue that will attract more dirt) and, with the key OFF, use the straw that comes with the contact cleaner to spray it into the hole in the bottom of the switch assembly below the Start button while working the button vigorously several times, then turn the key on and see if the light has started to work (you may have to repeat this 3 or 4 times before the contacts are clean enough to work again). If that doesn't fix it you will need to open the switch assembly (screws on the bottom) and try spraying the contact cleaner in from above (same drill: spray/work button/test/repeat) and if that doesn't gve results you might even have to disassemble the btton and use a brush and more contact cleaner to scrub the parts.
NOTE: DO NOT use sandpaper, emery cloth &c for cleaning contacts. Aside from removing any plating on the contacts, particles of the grit can become embedded in the copper and chew up the mating contact.

BTW: "short" (AKA "short circuit") is a technical term for when wires touch (allowing the current to take a short cut). Shorts usually result in blown fuses. What you are looking for is actually an open circuit (break or interruption in the current path). Opens rarely blow fuses bit almost always result in something not working.
 

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Discussion Starter #9
Yes, I have the correct wiring diagram. I am pretty sure I found it on here. Has been a huge help so far in just understanding how this thing all fits together. The shop manual will be a huge bonus though. I'll go grab that and start reading it over.

Thanks for the correct term on short vs open. That makes sense that it's technically not a short. I was able to plug the headlight in and use the the power supplied from the blue and white wires on the bulb and jumped the ground directly to the frame and that worked. I will trace that path around and see where it is breaking contact and hopefully fix from there. It worked on bright and dim settings via the switch, so that is working although it is very dirty inside. I will clean it while I have it disassembled make nice and shiny and hopefully get it road worthy here before the weekend.
 

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OK, it sounds like the problem is n the ground then. Is the green wire from the headlight plug plugged into the green from the main harness? (you'd be surprised how easily that can happen)

If you do end up adding a new ground connection remember that the primary return path for all electrical circuits is the green wire in the wiring harness, not the frame and that chassis grounds are notoriously unreliable. And whatever you do don't ground it to the headlight shell (or ground anything to the forks or triple clamps or anything ahead of the steering stem for that matter) because that would require the current to flow through the steering head bearings to return to the battery and any time the steering was turned slightly tiny sparks would occur between the bearings and their races which would eventually cause pitting.
 

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Discussion Starter #11
I'm at a complete loss now....

I opened the wiring harness to the left handlebar. Cut the wrap off to make sure it was all ok. The wires look good and I jiggled a lot to see if I could figure out which one was causing my issues and had no luck.

I randomly grabbed the clutch cable and jiggled it and my headlight went off and on. The more I played with it, the more it seems to be that, which makes no sense to me at all....

Still makes me think it't a grounding issue, but that just seems weird.

Any helpful advice there?
 

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Wiggling the cable probably moved the wiring harness a bit that leads inside the headlight bucket. Inside the bucket, at the back of it you'll find a tab welded to it for a ground wire. Check and see if green ground wire is loose or just laying against the metal inside it somewhere.

DSC_5090.JPG

Also check the wires at EACH plug inside there. I've seen several times where the wire looked like it was ok on the outside with the plastic cover of the wire, but the wire inside it near the connection was broken or pulled loose. If you pull on a wire where it goes into a plug, the plastic cover will stretch if the wire is broken inside. If it's not broken you get no stretch. You could also pull on each green wire at all the plugs and see if that makes the light go on and off.
Good luck and hope this helps. Wiring isn't fun.
 

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Discussion Starter #13 (Edited)
Wiggling the cable probably moved the wiring harness a bit that leads inside the headlight bucket. Inside the bucket, at the back of it you'll find a tab welded to it for a ground wire. Check and see if green ground wire is loose or just laying against the metal inside it somewhere.

View attachment 174549

Also check the wires at EACH plug inside there. I've seen several times where the wire looked like it was ok on the outside with the plastic cover of the wire, but the wire inside it near the connection was broken or pulled loose. If you pull on a wire where it goes into a plug, the plastic cover will stretch if the wire is broken inside. If it's not broken you get no stretch. You could also pull on each green wire at all the plugs and see if that makes the light go on and off.
Good luck and hope this helps. Wiring isn't fun.
Ok. I checked everything that I could. All wires are ok as far as I can tell. That ground inside the headlight is secure and didn’t make a difference when I ran a jumper

However this seems to be the problem.



There are two wires next to the clutch handle. Green and green/red. One goes to the horn and makes some kind of ground loop I believe. Not 100% sure there.

From the wiring diagram it looks like they are connected to the horn switch and is itself possibly the starter disconnect switch? I can see part of it connected to the horn switch since I took it apart, but I am assuming they just share a common ground.

I ran a jumper between those two and was able to get full headlight without any issue. Jiggled and all of that and headlight stayed on. I’m assuming something in there or where they mount to the handlebar has some issue?


Sent from my iPhone using Tapatalk
 

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Your picture shows the clutch switch. It prevents the bike from being started with the transmission in gear unless the clutch is pulled. It should have a green wire ( ground) and a green with red tracer wire. The green/red wire goes to the starter solenoid and also to the neutral safety switch via the neutral indicator light. There should be no connection with the horn.
 

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Discussion Starter #15
Your picture shows the clutch switch. It prevents the bike from being started with the transmission in gear unless the clutch is pulled. It should have a green wire ( ground) and a green with red tracer wire. The green/red wire goes to the starter solenoid and also to the neutral safety switch via the neutral indicator light. There should be no connection with the horn.
They just share ground as far as I can tell.






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Yes, that is what the wiring diagram shows. The green is a ground wire.
You wrote "...I ran a jumper between those two and was able to get full headlight...". Which two did you connect with the jumper wire?
 

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Discussion Starter #17
I ran a jumper between the two wires for the clutch switch.

I think I found my problem though. I unwrapped the whole wiring loom and found a few wires that look iffy. Going to replace those and see if that solves the issue.


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Discussion Starter #18
All solved. Thanks for the help everyone.

Ended up just pulling all the black harness wrap off the bike and looking at each group of wires. Found a group where the grounds (3 of them) were pinched and had been broken inside. Got them wired back together and all is well with the world.

Gotta love old bikes and 40 year old wires!!
 

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Discussion Starter #19
Well, all of that and it WAS working. Worked great Saturday night and then I ut it all back together Sunday and now I have no headlight again:confused:

This time I have no power coming to the headlight or the fuse for it.

No idea what I could have possibly done, so it would seem I am going to go back wire by wire. Seriously. I'm about ready to just wire up my own headlight switch somewhere else....

I just want to ride the dang thing....
 
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