Headlight turns on with brake?!?!

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Jun 14, 2007
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Okay, this may be my wildest question yet.

I have a three position ignition switch - off, ignition on, and ignition and lights on. Headlight runs on a relay.

Just noticed that when ignition only (not headlight) on, using the brake will turn on the headlight (either high or low beam, depending on where dip switch is at the time).

Digging out the multimeter, but in true BrianK fashion I figured I'd start the quest for knowledge by seeing if anyone ever ran into this before.... :oops:
Hehe, had sorta similar, but played out via the parking lamp in shell
and signals.
I'd suspect a ground return reversal path into lamp and switches or

Another fairly common occurrence is to get a brake wire short
that kills ignition when brake touched.

A feature indeed Dave. If only I were selling the bike, I'd hype it to the stars. Kind of a safety feature - like a modulator!

Hobot, help me a bit more - play out that ground reversal theory of yours? How exactly would that work?
I think that he means you could have a bad ground in your brake light circuit. The brake light is finding the ground through the headlight (or tail light).

Hehe, if likely such unplanned electric light show features,
Install LED signal kit by BulbsThatLastForever, and put in
non resistance plugs on plain copper HT leads,
They become stem mounted timing lights, in sync with engine
blips, but also syncopated to the normal flashing rate.

Quite the attention getter at vintage rally or any where.

Ha ha I only sound like I've a clue on your mystery current flows.
Girs, idea is more specific than mine, but made good sense
trying envision what would do this.

Brake light switches should be their own circuit separate
from running and tag light and head light.
IIRC, brake switches have power ran to them, when closed,
sends it on brake filament then into shortest ground path
to battery. But may be other way around power always
at brake filament just waiting to connect to ground though
brake switch closing.

Then again its easy to cross power wires with grounds
in head lamp shell, so let us know how it turns out.

I had a car once that honked its horn when you used the turn indicator. I attracted a lot of attention at intersections. Sadly this type of safety feature is not readily understood by the general public and I got a lot of rude hand gestures.
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