Power on ground?


XS400 Member
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Lompoc, CA
Hey guys
I've got an 80 xs400 G with power on black wire in light/indicator controls. Not sure what's going on here. Any help appreciated. Thanks
This might be normal (if you pulled the wire off of its grounding point and the switch upstream is on), or it might be bad. More info would be needed to help.

What problem is causing you to test it?
Where is the end of the wire you are testing located?
Is the wire plugged into something, is it just "floating", or is it normally attached to the frame?
Have you traced the wire to an upstream device?

The wiring diagram for the G/H/J bikes is pretty good, so it should be pretty straight-forward to figure it out.

Welcome to the forum, BTW!
Thanks for getting back to me
I'm trying to get power to headlight and trace power back to left hand control using test light. I opened control to see if wires are soldered on in good shape, I noticed I'm getting power on black ground wire. Not only on wire but on control housing as well. Is this normal? I don't see any frayed or loose wires so im confused. Turn indicator s work but no headlight. And yes light is good, lights up on separate power source. Any ideas. Thanks
Great details. Yes, I have ideas on what you can do.

Let me get out the wiring diagram when I get back this evening, and I will get you some next troubleshooting steps.
Looking for possible electrical ground issues is always a good thing to do. But, when I look at the wiring diagram, the black ground wire in the left-hand switch gear is either from the clutch switch or the turn signal switch, so probably not causing your head light problem. This still may be an issue, but we will get to that in due course.

It is good you have verified the headlight is operational as the starting point. There are some other components in the circuit that might be causing your issue. If you trace the current path backwards from either the yellow (high beam) or green (low beam) wire, you get to the light dimmer switch, which is in turn powered via a blue with black tracer wire by the headlight relay. This relay gets power from the 10amp headlight fuse and also receives a signal from the alternator via a diode that the engine is running. If the engine is running, the relay with turn on and send power to the headlight.

Of these components, the easiest thing to check is the headlight fuse. Verify that there is 12VDC to the fuse when the main switch is turned on and check continuity across the fuse terminals (do this even if the fuse looks visually good) either by using an ohm setting on a multi-meter or by checking that you have good voltage through the fuse with your test light.

After the fuse, find the headlight relay (it is one of the two similar looking relays under the front of the battery box). The relay will be the one that has a plug with white, black, blue with black tracer, and red with yellow tracer wire. Pull the plug and verify that the red with yellow tracer wire has 12VDC on it when the main switch is on.

If these first tests are fine, then checking the relay is next up, but let us know how this stuff goes before we go to into that.
There were some bikes that used AC power to the headlight through a diode to convert it to dc. If the diode went bad, it may cause odd readings. Not sure if that helps and hopefully a more knowledgeable member can chime in.
Wow. Thank you both Capt. And Testid. I will go back and look at these wires. Good hint about the alternator power did not know. I will take this info, take another look and get back to you. Thanks again!
On your bike, the alternator does not power the headlight directly, it only supplies a "signal" to the headlight relay. The relay powers the headlight with DC from the fusebox.
Ok. Got it. Well, been at this thing for hours looking at wires and diagrams and connections. Im out of ideas.
Just to further clarify im getting 12v on black( ground) wires except wires directly ground ed to frame and battery. Now im getting this reading while the bike is static with key on. The bike does run but doing testing with fresh new battery. Lithium ion
With modern reg rec. I replaced original reg rec but no change.
I think what I'll do is bypass all grounds in loom and run new grounds independently and direct to frame/battery. We'll see, thanks for info and please reply if any ideas cheers!
After rereading the post If you are getting 12 volts on the black wire(assuming that it is and should be ground)you most likely have a bad ground connection somewhere.
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Hello , yes I agree. What I ended up doing was to run my own ground wire bypassing the original ground. I didn't want to take apart the harness that would be a nightmare. So far so good. In fact it's much better, lights are nice and bright everything works well. We'll see! Thanks for the interest!
I'm new to forum and I thinks it's a great resource I've learned much. Cheers!