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Discussion Starter #1
Good morning, all. I recently did some work on a '80 CB750k. Among other things I cleared the triangle and moved all the electrical into a sheet metal box that I made and tacked onto the frame. Since then the headlight, taillight and brake light are not working. I've done some basic troubleshooting, e.g. fuses, obvious breaks in the harness, etc. I was about to start on the switches, but thought I'd reach out to the collective to see if I'm missing something obvious. Thanks.
 

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Have you tested resistance between power leads and the frame or metal box you made?

I am assuming it was all working prior to the modifications so that kind of narrows it down to something you changed. You could have shorted something out when moving things around. But my first guess would be that something is grounding out where it shouldn't be
 

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the obvious would be a fuse, since all lights are on the same circuit and the fuse is the central junction point. did you actually take the fuse out or test it with a continuity tester?

is your sheetmetal box getting hot when the key is on? it could be you have shorted to the box. Otherwise, get out the continuity tester and the wiring harness and start testing the sections of wire between the headlight, switch, fuse block, etc.....
 

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Along with a pocket tester checking continuity, etc.....sometimes I unplug stuff and use leads from the battery to bypass sections of the harness to eliminate obvious items. Assuming everything worked before the modification and now nothing works after the modification leads me to believe you may have a grounding issue or a problem with the switch.

Good luck and let's see some pics of the modifications.
 

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No updates from OP? Are you still having issues?
 

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on any older bike it is pretty much a must do
this work i tell of
and that is unplug from each other every terminal conection multi-pin or single
do it one at a time take your time cand be methodical
it isd a hateful tediuos job but only needs doing once on each bike
carefully inspect and clean all ground terminal ends
if any doubt about condition take key switch apart and clean contacts
if you have the cylindrical glass fuses you must assure they are still breing held firmly bu the brass deals crimped to wire ends
a common issue is somebody puts in a 100wat headlight
or asdds a second 55 job and it will overheat the connection ast each fiuse end and this also anneals thge brass so it looses spring tension clamping effect causding a poor connection with high resistant generating heat and on it goes in a snowballing whirpool of perpetual fail
examine them clean them and tweak the femal to ensure a tight fit
better yet use modern fuses
assemble them with die-lectric viener schlider
 

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Discussion Starter #8
Four screaming kids in the house took me away from checking this forum, but I'm back. I'm going to check each fuse independently of the fuse box tonight. As far as the sheet metal box heating up - yes, the rectifier got hot as shit and melted my wires into the alternator. I've addressed that problem and moved the rectifier (any ideas for insulating it from surrounding parts?) Never thought to check resistance to the box. Will try that also. The horn still works, and all other electrical appears to be in good working order. Speaking of fuses- when I first started troubleshooting this problem I noticed one of the fuses was burnt out, so I replaced it with the spare. The fuse is "seemingly" functioning as intended, but as Geeto suggests I will test each fuse separately. For argument's sake if the fuse is blown what would be your first line of inquiry? Thanks, all!
 

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Four screaming kids in the house took me away from checking this forum, but I'm back. I'm going to check each fuse independently of the fuse box tonight. As far as the sheet metal box heating up - yes, the rectifier got hot as shit and melted my wires into the alternator. I've addressed that problem and moved the rectifier (any ideas for insulating it from surrounding parts?) Never thought to check resistance to the box. Will try that also. The horn still works, and all other electrical appears to be in good working order. Speaking of fuses- when I first started troubleshooting this problem I noticed one of the fuses was burnt out, so I replaced it with the spare. The fuse is "seemingly" functioning as intended, but as Geeto suggests I will test each fuse separately. For argument's sake if the fuse is blown what would be your first line of inquiry? Thanks, all!
you really should not have fucked with the electrical system ,pardon my language
it was already located in the best possible location
all you have done is tossed a giant red hot monkey wrench into the project
i know everybody else does it but if you had asked first we could have stopped the madness,prevented pandora's box from being opened
see,there is absolutely no reason to do what you did
it only will cause problems,putting everything in a small box is not a smart thing to do..... why not just get it over with and dowse the bike with gasoline and toss a match on to it now
 

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Discussion Starter #10
Where's the fucking fun in that? (Pardon my English) If I'd wanted a perfect stock bike I would have bought one. I've heard this piece of advice before and understand it, but when I bought a 40 year old bike to do with as I saw fit I had a good reason, e.g. to make mistakes, and learn from salty veterans such as you appear to write like. I've been off this forum for years, and I know Geeto has a similar view as yours, and you're both not wrong...we just have a difference of opinion.
 

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Discussion Starter #11
I just reread my last post and realized I sounded more edgy than I meant to. I appreciate all feedback - whatever form it comes in.
 

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Discussion Starter #13
It's not the fuses. .. Just ran continuity test on all of them. Will check sheet metal box and other possible grounding issues next.
 

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Start from the alternator :/ there should be 3 probably yellow wires coming out of the engine very close to the alternator and each of those should have some measurable resistance between the wire and a good ground ... probably in the realm of just a few ohms.
If none of your fuses are blown then the assumption is that you do not have a direct live short to ground, you are looking for a dead short.

... what fuse burned out earlier? that circuit is the one to suspect most.
 

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... cleared the triangle and moved all the electrical into a sheet metal box that I made and tacked onto the frame. Since then the headlight, taillight and brake light are not working. ...
If you burnt out a fuse at this point that really does imply that you mixed up a ground wire and a hot wire,
would be wise to make yourself a new wiring diagram based on what you have right in front of you now while you are tracing back each wire.
 

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Discussion Starter #16
One fuse blew...? Didn't have the foresight to note that. Just checked the brake light against the box and I'm getting some resistance.
 

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Discussion Starter #18
The three wires out of the alternator all have measurable resistance as you predicted. Should I be focusing on the brake wire as I've found resistance against the box?
 

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That test would imply your alternator windings are good, even better if the reading was in spec :/ what was the resistance? There will be an acceptable range noted in the service manual.

Some measurable resistance on the hot wire side is good, that implies you don't have a short and what you are measuring is the resistance of the bulbs, if you were to remove the bulbs from that branch, that resistance should go infinite.

Ground wires and parts on the other hand should have zero resistance between the battery ground and almost anywhere on the motorcycle you can touch the multi-meter lead to without pealing back hot wires.

... you're not going to all of a sudden tell us that you converted everything to LED, right? LED uses diodes :/ everything changes.
 

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Discussion Starter #20
No LED's. I'm in incandescent man from way back. How do I know which wire is the "hot" wire. I believe on all Hondas the green wires are ground, but some of the wires have green stripes on them. For example the taillight has a white wire with green stripe, and a green wire with a white stripe.
 
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