Headlight shorts Brake light

[kungfutoast]

Help!
I am scratching my head over here. Maybe someone can shed some light on my problem.

I have a very basic wiring harness on a KZ750b. (See diagram)

When I turn on the headlight my brake switch stops working. I have tried every combination of wiring. Tried to reroute the switch to different circuits etc. Has anyone had this problem or know the solution? It's probably some dummy thing staring me in the face.

-Thanks

[jbswear]

Your diagrams look like they should work.

But I doubt that your circuit actually looks like the diagram.

Are your brake and headlamp wired in series? If so, that's a problem. They should be in parallel.

[jbswear]

I have a very basic wiring harness on a KZ750b. (See diagram)


Which diagram? Both are wired differently, but both should work properly.

[Pendulum]

Are you sure that your brake switch is inline, and not going to ground?

[jbswear]

Also check your grounds. Again.

Then run each circuit on its own. You have a short or a bad connection somewhere.

[kungfutoast]

Thanks for the follow up.

I have tried both options. Plus many others. This set up wields the best results.

There are subtle smiley faces that show the results of each option.

Not pictured is an inline on/off switch at the headlight.

In diagram 1 the headlight works but the brake light filament does not turn on when applying the brake.

In Diagram 2, the brake light filament will work if the headlight is turned off. If I unplug the headlight entirely I lose the brake light function. Likewise, if I remove the headlight switch, keeping the headlight constant I lose the brake light function. Only when I have the headlight plugged into the ignition switch (pictured) and in the off position at the inline toggle switch does the brake light filament turn on... Oof that's the closest I have come to having both headlight and brake light working.

Thoughts?

[jbswear]

Scrap your diagram.

Pull your wiring.

Redo it. There's a mistake in there that you cannot find. If your wiring matches EITHER of those diagrams, it will work.

Your wiring is done incorrectly.

[nomoney]

Scrap your diagram.

Pull your wiring.

Redo it. There's a mistake in there that you cannot find. If your wiring matches EITHER of those diagrams, it will work.

Your wiring is done incorrectly.

This.

Your diagram shows your lights to be in parallel correctly.

Does your headlight switch also turn on your rear running light?

[kungfutoast]

No, the switch only turns on the headlight. I just ran a test without the inline switch. In the ignitions accessory position, headlight is off and the break light works. In the second position, (on) the headlight is illuminated and I lose brake light function.

I just rewired the bike. Fresh everything not reusing any wire. Sanded my grounds to raw steel and mounted them at different points and tested them. I am still having this issue. Plus I am out of wire and connectors.

Let's say, for the sake of this discussion, my wiring is sound. What would other issues be? I have replaced the ignition switch, and tested two other tail lights plus one other head light. All giving the same results. Would it be safe to assume the brake switch is at fault?

[jbswear]

If your wiring were sound, you wouldn't have this problem.

Sorry, man, but that's it.

(edit)

If the brake switch is simply on/off, with no ground, then it *can't* go wrong, aside from being always open or always closed.

[kungfutoast]

You would think. Thus my total confusion. Well, thanks for your help. If I do find the problem I'll share.

[Sky]

Shot in the dark, does the tail/brake light a two wire or three wire style? If three, sure you've got the right wire to ground?
I've also sen people mix up the headlight wires and get some strange results.
Keep in mind japanese, chinese and American wire color schemes are totally different.
I'd keep the lights and ignition circuits separate, esp the headlight. Some like the brake light wired with ign though, that way you don't forget to turn it on
Hey your batt is fully charged, right?

[UncleMonkey]

Try this. But it sounds like you are using the wrong wire to ground your brake light

[DustyDave]

Try a wire from the tail light bulb base not the socket to the battery negative. I suspect that because of a bad ground the dual element tail light bulb is feeding back to the headlight to ground enough to light but can't feed back when the head light is on. Both elements of a dual element bulb tie together at the ground pin, so if there is no ground the current flows through booth elements and back up the tail light power supply wire and eventualy to the head light which won't light at such a low current but will ground the brake light enough to light the bulb.
Dusty

[kungfutoast]

Yeahoo! Thanks Dusty! Sure enough The ground wire to the tail light was in bad shape. Soldered one to the bulb housing and mounted to the frame and viola! Thanks a billion.
-Dominic

Try a wire from the tail light bulb base not the socket to the battery negative. I suspect that because of a bad ground the dual element tail light bulb is feeding back to the headlight to ground enough to light but can't feed back when the head light is on. Both elements of a dual element bulb tie together at the ground pin, so if there is no ground the current flows through booth elements and back up the tail light power supply wire and eventualy to the head light which won't light at such a low current but will ground the brake light enough to light the bulb.
Dusty