Healight/Tailight issue. Help!

So, just the other day my 78 kz650 headlight and taillight stopped turning on, but the brake light was working fine. The bulbs are definitely not blown and when i fully charged the battery, nothing changed. However, the brake light now remains on all the time even when no pressure is applied to the rear brake (front brakes are not hooked up).

so...battery is charged, brake light works, everything is grounded, none of the wires seem burnt or shorted.

My extremely amateur theory is a faulty rear brake switch causing problems?

Most bikes have two(2) brake light switches, try disconnecting one to see if it's causing the problem, if not, reconnect it and disconnect the other.

The front switch may be the type that works on brake pressure,or have a small actuation switch built into the front brake mount(perch).

Vibration may have moved the rear brake light switch out of adjustment, so check the hardware(lock nuts on the switch body).

KinkJayRoe wrote: So, just the other day my 78 kz650 headlight and taillight stopped turning on, but the brake light was working fine. The bulbs are definitely not blown and when i fully charged the battery, nothing changed. However, the brake light now remains on all the time even when no pressure is applied to the rear brake (front brakes are not hooked up).

so...battery is charged, brake light works, everything is grounded, none of the wires seem burnt or shorted.

My extremely amateur theory is a faulty rear brake switch causing problems?

Brake light is an independent circuit which should not cause a problem with the headlight or tail light.

The front brake light switch has a "hot" brown wire. Activating the switch connects the hot brown wire to the blue wire that feeds current to the rear bulb's brake filament.
Same for the rear brake light switch.

Failure of head light and tail light might be due to insufficient grounding (for whatever reason) through the black-yellow wire; or might be due to corrosion inside the ignition switch, headlight switch or dimmer switch. Or might be due to a blown fuse or other reason for not receiving current (such as a loose connector, or broken internal wire, or whatever).

This link will allow downloading a wiring diagram from KZrider's FILEBASE, which should help trace the current flow and find a break somewhere between the battery positive terminal and the headlight bulb:
www.kzrider.com/filebase/doc_download/290-z650b2-c2

Good Fortune!

I'd suggest getting that front brake working or lighting will be the least of your problems. The front brake supplies roughly 80% of your bike stopping power. Ed

Inside or right behind the headlight is a big plastic 9 pin connector that controls a lot of the lighting functions. Try unplugging it, spraying it with contact cleaner and reconnecting it. A little dielectric grease on the female connector might help too.

I appreciate the concern! The front brake is fully functioning, I just do not have it wired to the brake light.

Disconnect Blue conductor from rear brake light switch...
Brake light go OFF...?
If so, switch is activating... either bad switch (old) or you still have enough spring tension activating it. Re-insert blue conductor and disconnect spring to test theory if tension activated...

Otherwise, blue conductor to rear brake light is some how picking up 12Vdc (battery voltage) in your harness/connections.

Red = +12Vdc from ignition switch to bulb (Running light)
Black'Yellow = Ground (Battery (-) / grounded frame)
Blue = Brake light switches, switched +12Vdc to bulb. (Brake Light)