Topic: Intermittent Headlight

[Chris Schneiter]

I have a '76 CB750 K whitch has had most of the bugs exterminated. It's newest trick though is that the headlight has begun to work intermittently, and now seems to have quit altogether, frustrating, because I love to ride at night. At first, the lights would come on after I wiggled the dimmer switch, then sometimes after I wiggled the front brake lever, then only after it had run for about 10 seconds and did the above. I have run continuity checks on I think everything, the tail light works,as do brake lights and blinkers, and the bike runs really well otherwise. The only tip off is that when I checked the fuse block last week, it didn't seem to have power except for the bottom fuse. Does anybody have experience with this? The fuses were fine. Is the middle fuse for the headlight? I plan to run more tests tonight....wiring problems make me superstitious...maybe I should spin around three times and throw salt over my left shoulder befor starting?

[eldar]

Well with wiring it is so hard to say what is wrong. Check the fuse block and make sure the contacts are clean and tight. Then trace all the wiring for the headlight.

From how you describe things, it sounds like a problem with the switch.

[Chris Schneiter]

Ok. an update for the headlight impaired...I think I may have my problem traced down to the headlight cutoff in the starter switch...last weekend, I tore apart my right grip..no evidence of corrosion or brake fluid damage, but I gave the starter button a shot of WD 40 (whether that was the right stuff to use I don't know)...Today, when I started it up, the starter button stuck a little, so I pulled some and banged on the grip...as I rode to work, I looked at my windshield, and my headlight (which hasn't worked in two weeks) was working, but going on and off when I hit bumps..when I stopped, it was off, but came back on when I banged on the grip again..I think I'm going in to check it out...

[TwoTired]

WD-40 is not plastic friendly.  If there is still plastic inside the control housing, clean/flush it with alcohol.

But, it sounds like you will have to replace the starter switch and/or wire a bypass to restore reliable headlight operation.

I'm guessing it won't be long until the starter button won't function anymore either.

[Chris Schneiter]

I figured it out! There is a headlight cutoff switch in the starter button that turns off the headlight while the starter is engaged. Last night, after starting, I pulled out on the actual starter button, and the headlight came on and doesn't even flicker! The switch only cuts the power to the headlight when it's depressed (and apparently also cuts power to the fuse block), and I think what's happening is that the spring in the button may be mashed down or is wearing out, so after starting, the button isn't returning to it's original position fully, allowing the starter to shutoff and the bike to run, but not far enough to let the headlight come back on...it's much more simple than I was making it out to be...I can live with it now that I know what's causing it, and as soon as I can, I'll either replace the starter button switch, or see if I can fix the spring.

[computerpulse]

Hey I have a 74 CB750K4 with the same problem.  Is this going to turn out to be the same problem?  I have no voltage at the fuse block for the headlight.  Everything else works fine.  Cannot get my headlight to work.  Any help would be greatly appreciated.  I tryed using a K4 wiring diagram to trace out but found the colors are not matching.  Where the schematic states 2 red wires going to the fuse block for the headlight, I have 2 brown wires instead.

[Chris Schneiter]

Yeah, I've been driving myself nuts with the Volt Ohm Meter tracing every wire on the bike..I think what's happening is thet when the starter button doesn't spring back far enough to allow the light to come back on, it kills power from the fuse block on out. Try pulling gently on the starter button and see what happens...mine comes back on and doesn't even flicker when I hit bumps. I think I need to stretch out my spring in the switch or get a new one, or a new switch.

[computerpulse]

I have 12+ volts to the lamp but when I attach the lamp I loose my voltage at the fuse block for the headlamp.  I am not sure what's going on.  The lamp is good and when I apply 12 volts to the fuse block the headlight comes on.  Something is kicking off.  Any ideas?

[TwoTired]

Any ideas?

Have you checked your starter push button switch in the right hand bar control housing?

[computerpulse]

Yes these are fine.  Seems to me the wiring colors are the problem.  I pulled the wiring diagram and followed all the wires from the fuse box to the switches etc.  I have a open brown and red that was one side of the fuse and a brown and white.  So I tied these two together and it worked but now my marker lamps don't turn on.  When I switch on the headlight, are the blinker lights both front and rear supposed to light? or just the front or neither?

[TwoTired]

The front bulbs are dual filament and the weaker filament should go on with the headlight, but off when the brighter filament is winking.

There are no amber marker lights allowed on the rear of US vehicles in many states.  The rear signals are single filament and wink only.

[computerpulse]

Thanks, must still have something wired wrong.  I had to make a jumper to go from a brown and white I had open to the brown and red I hooked for the headlights to work.  Also I don't think my headlights light up as bright as they are supposed to.  Still working on it.