• Enter the March CB750 Supply gift certificate giveaway! It's easy... Click here, post something, and you're entered into the drawing!

1981 cb750f headlight doesn't turn on

visorclown

CB750 Member
Messages
24
Reaction score
0
Points
1
Location
United States
My front headlight won't turn on. I just bought a new one hoping the old was bad, but no luck. All connections seem to be tight and proper. All turn signals work as they should. I cant figure this one out. I'm no electrical expert by any means. Is there a diagram for the electrical? Any help would be greatly appreciated as I can't get a safety inspection till I fix it! Thanks for the help.
 
Hey Buddy, I'm a noob here myself. Have you unplugged the plug to the headlight and put a volt meter probe on the main pin of that plug with the power on to verify power to that point? I have a 76 cb 750 f and I believe mine has a dedicated fuse for the head light.
 
Well, I did try that. It didn't seem to be getting any power. However, I'm not even sure I tested it properly. Electrical is not my thing i dont see any fuses around to check or replace. If you've got ideas let me know. Thanks!
 
Thanks for the diagram. It's easier to read than the other ones I had found. It seems that the lines in question are the blue and white that go to the dimmer switch. Is the dimmer swith the start button? This is where I'm lost.
 
No, dimmer switch just changes between hi and Ko beam filaments in the headllght. It's kind of hard to see and your eyes might be as bad as mine. In case you don't already know, try pressing the "control" and "+" keys at the same time to zoom in.. ("control" and "-" zoom back out).

Look straight up above the right hand horn signal... see the "BAT5" and "BAT2" and "ST" terminals. Pressing the starter button closes BAT2 to ST which closes the starter solenoid... and the bike should start. It's the Y/R wire that carries the juice to close the solenoid.
 
Ok i do see that now. I guess I'm not seeing the connection with the headlight. Aren't the headlight wires going to the dimmer switch? I thought ib read on another post that another guys headlight went out because of a bad starter button. One guy said he had a bad hi/lo switch. Not sure how to rectify either of those situations.
 
The headlight connections are the B and W wires... one is high, the other low... and the ground wire of course.

Look straight above the left horn symbol and above "switch".
 
Right, so I located them, but how does one determine the breakdown? Is it at the hi/lo switch? Is it at a connector? I've traced the wires and opened up the boxes and there's nothing obvious to the untrained eye.
 
unplug the blue wire from the headlight connector. turn the ignition switch on. Touch the blue wire from the headlight to a black wire in the headlight bucket (there's a connection of black wires that go to the turn signals that will work, just be sure you use the hot side if you have to unplug the wires to get to it,,, there may be an extra place on the terminal though)

If the turn lights work (before maybe disconnection one at the black wire) but the headlight doesn't work when touching the black wire, the problem is likely in a bad connection, including a bad ground. If the headlight works, the problem is in the headlight circuit including a fuse, the hi-lo switch, or bad connections including ground.
 
I actually had everything open and testing when you responded. Nothing works when touching the blue wire to any of the black wires.
 
You had the key on, right? And the only thing that doesn't work os the headlight?

Connect a wire from battery positive to to the blue wire at the headlight. Check the white the same way. If it doesn't come on, connect a wire from battery negative to the green wire from the headlight at the same time.

If you go straight from the battery to the headlight leads and it doesn't work, the problem is in the connector or maybe a broken wire, or the headlight is no good.

If nothing works, go from the battery to the light terminals to be sure the light works.
 
I'm not exactly sure what I did, but now all the sudden none of the signals work. I can't imagine that I did anything to affect all that. I had to stop the convo for a while because I needed to get out and ride while we had 66 degrees on Feb 8th! I think I'm gonna take it to a buddy of mine to give it a look. I've got some carb syncing to do as well as a few other minor things. The electrical is a headache I'm not willing to get into. Although I know I should. Thanks so much for the back and forth dialogue today tommycarl! That was so awesome of you to step in and lend your knowledge.
 
Well if you unplugged the black wire(s) as we discussed, I would suspect that to be the problem area with the turn signals. With all the wires in that bucket, it's sometimes hard to be sure you have them all plugged in, and even sometimes easy to unplug one again. As for the headlight, I'm thinking that it's something simple but hard to pinpoint... like a bad ground, bad connection, or maybe even a wire unplugged somewhere. Lots of potential sources for the problem and plenty of patience required. Nothing particularly hard about it until one gets frustrated... then it's nearly impossible!
 
That's exactly what I'm thinking! I don't have the patience or know how to trace wires and check all possibilities. Thanks again for your help!
 
Back
Top