Headlamp question

The headlamp on my '79 KZ750 went out on the ride home tonight.

I'm trying to figure out if it is just the bulb or a short somewhere.

When these bulbs go out, do both the high and low fail at the same time?

Not normally, although I'm sure it's possible. This is a good thing as I once had my highbeam go out at night while riding on a dark winding road - thankfully switching to low beam saved my bacon (not to mention other parts). Ed

Hmmmm... It went out right when I flipped the switch from low to high beams. Then neither one would work.

I'm thinking either the bulb went or I've got a short in the switch.

Check your fuses, make sure power is going across the fuse for the headlight, then test for power at the bulb socket. Then you can also check the ground while your at the socket end.

Ok will do. I had running lights, brake lights and blinkers so I don't think it's a fuse.

If it's not a fuse, the next step would be to disconnect the headlight wires and check them with a multimeter set to 20v DC and your ignition switch in the ON position. If you get power there, then it is either the bulb, or the ground.

Looks like a separate fuse, 10 amp, for the headlight.
www.kzrider.com/filebase/doc_download/284-z750b4

Motor Head wrote: Looks like a separate fuse, 10 amp, for the headlight.
www.kzrider.com/filebase/doc_download/284-z750b4

In that case, before replacing the blown fuse, follow the wires from the headlight to the handlebar switch, and from the switch to the headlight fuse. Look for any exposed wire, or damaged heat shrink around the connectors that may be touching metal. You may have a short in the system that grounded and blew the fuse.

EDIT: It's possible that the short is inside the handlebar switch itself, so it wouldn't hurt to pull that off and inspect there as well.

It's easy to check if the bulb is ok. Do continuity check between the low beam terminal and ground terminal on the back of the bulb, then do the same for the high beam terminal. Ed

Motor Head wrote: Looks like a separate fuse, 10 amp, for the headlight.
www.kzrider.com/filebase/doc_download/284-z750b4

I've got that diagram in my manual but I gotta tell you, I have a helluva time decifering it. Now that you pointed it out, I can see that one of the 10A fuses connects straight to the hi/lo beam switch.

It could be as simple as a loose ground wire, or corroded connector in the ground circuit. I would check that as well when checking the wiring near the headlight itself

Topper wrote:

Motor Head wrote: Looks like a separate fuse, 10 amp, for the headlight.
www.kzrider.com/filebase/doc_download/284-z750b4

I've got that diagram in my manual but I gotta tell you, I have a helluva time decifering it. Now that you pointed it out, I can see that one of the 10A fuses connects straight to the hi/lo beam switch.

Those Old glass fuses can Look good, but do to heat lose the connection to the end cap.