headlight no go

[Andy De]

Hi, my son's 81 cb750 custom has just lost its headlight. My son without checking the lamp bought a new one and installed it,without success. I have not checked anything other than his old bulb for continuity. It looks like his old bulb is okay. I'm not sure of fuses for the headlight and it could be the switch? Any other ideas? Any help would be very much appreciated.

andy

[LukeM]

It should be easy to check the socket for the headlight with a voltmeter.  One pin will be ground, and the other pins will be for low beam and high beam.  Get ahold of the wiring diagram for your bike (you'll find links for that on this site), turn the key on, and measure away.

If your voltmeter is also an ohmmeter, you can check the continuity of the new headlight element as well.  It's hard to believe it's defective from the store, but it does happen sometimes.

I'm also wondering if there's something unique about the lamps used for motorcycles.  I can't think they'd be that different from the automotive models, but you never know.

Wow...a whole lot of vagueness in this post.  I should be more positive...or maybe not.

Luke M

[Andy De]

Thanks for your reply. My son bought contact cleaner and took apart the switch and cleaned it up and all the wires and connectors in the headlamp area including the ground. I tested the voltage to the lamp and got about 6.8 volts. It seemed like something was impeding the voltage. My son had earlier checked the fuses with a multimeter for continuity and all was good. I looked at the fuses and none looked fried whatsoever, so we thought it must be a short somewhere. Guess what, - I decided to check for continuity of the fuses and found one that was no good! I totally looked normal in every way! I simply took the spare fuse and put it in the headlight slot and all was good. My son swears he checked all fuses for continuity, but I think he missed one. Anyways, all is good and all contacts should be clean for quite a while

andy

[vern401]

If you get some electrical grease it wil help keep the connections from coroding again.

[LukeM]

Hmm..6.8 v is about half what the battery supplies. I'll have to look at the schematic to see where the fuse is in the circuit. I would expect all or nothing, but I've been wrong before. As long as it works, then that's good enough. :-)

I'm glad you got it working.  I agree with Vern that a little electrical grease will do wonders keeping the contacts clean and fresh.

Luke M

[vern401]

I didnt even think of the low voltage. Both elements work off the same voltage so you have corrosion someplace. It is probably in the hi/low switch someplace. give it a good cleaning and lube it with grease. Be careful not to loose the small parts in there. You may want to clean the horn button while in there. Next back to my memory is the Fuse. Actualy you may want to go through the wiring harness and clean&Lube all the connections you find. the regulator and rectifier make sure are clean and protected.
Let me know if this helps.
Vern