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Discussion Starter · #1 ·
I've rebuilt a '72 CB450. The PO did a little bit of tampering with the wiring harness (adding what looked like a non-functioning kill switch, and some sort of hacked running light). Bike ran before I torn it down. I removed those changes and had the harness looking like stock. I've rebuilt the bike and installed and connected all of the wiring. Yesterday I installed the battery, turned the ignition key, and...nothing. No lights, no horn, no starter...nothing.

Battery tested at nearly 13 volts, so it is good. It looks like power is running to the ignition switch, so that looks good. Beyond that I have no idea.

There are a myriad of other areas things could be going wrong, but I have basically zero knowledge. I'm sure there is a bad connection somewhere, or maybe one of the handlebar switches is messed up.

Can anyone point me in the direction of a simple, step by step overview of how to go about diagnosing the issue? Do I just start tracing wires from the battery out? How do I actually test those wires to find the culprit?

Would really appreciate any assistance. Thank you so much
 

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I have never worked on a 450 but the first thing to check and see if you have a good ground. If you dont have one you will need an ohm meter and a wiring dia. There are members on here that can help you with the dia. I also have a wire tester, any auto parts store about $10..00, This will allow you to test any wire without disconnecting it. Since you have no power any where I would start at the battery then the switch. Once you have power to the switch and still no power to the bike I would pull the switch and test it with the ohm meter. Maybe this will point you in the right direction .
Bill

I have never failed. I just tried a lot of things that didnt work
 

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Without a good wiring diagram, it is very hard to trace an electrical problem. Once you have that, we can lead you through points to check.

BTW, how do you know power is going to the key switch, did you measure it there? There is a fuse holder between that switch and the battery, which is often corroded, and, when the key is off, Voltage may be measured at the switch input, but when the key is on, the resistance of the fuse holder can drop it to near 0V. If power is still at the switch, check the solder on the wires at the back of the switch for cracks or breaks. The rest will need a diagram to follow, as I stated above.
 

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Discussion Starter · #4 ·

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Note the main switch (bottom center) IG wire goes to the foot brake light switch, horn, 'winker' relay, regulator, and starter relay, and also into the headlamp, which has the connectors all in a line on that diagram, and powers things on the left, like the front brake light switch. With the key on, does the horn work, or the brake light? Turn signals? It is fairly easy to check power at the horn, and the other side of the horn should go to ground when the button is pressed, assuming the ground wire is connected to the bars. If you have Voltage at the horn, but it doesn't sound when the button is pressed, you likely have a ground problem (the green wire that starts at the battery (-).
 

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Discussion Starter · #6 ·
Thanks Rick, right now with key on, nothing is working: horn, brake light, turn signals, etc. I'll be back at the garage tomorrow night and plan on using the meter to confirm power to each, and then will work on routing out if it's a ground problem. I plan on documenting this for others so there is a bit of a process to identify electrical issues on a stock harness after a rebuild.
 
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