Headlight not working

Hey guys. A while back, I noticed that my headlight would turn off whenever I straightened my handlebars. When I turned them all the way to the right or the left, my headlight would come back on again. I figured I must have a loose connection somewhere, so I pulled the headlight out of the assembly, but I couldn't find anything loose inside. So I put it all back together, but then the headlight wouldn't come on at all anymore.

Next I started testing things with my multimeter. I seem to be getting good connectivity from all of the fuses. The headlight itself also *seems* OK (neither of the headlight filaments look burned out, and the multimeter shows connectivity between the terminals). I tested my battery without the bike running, and I'm getting just under 12v (11.4v or so), so I don't think that's the problem.

I've been using a variety of wiring diagrams to try to narrow down the problem. This one seems pretty good:

http://cyclepsycho.com/yamachopper/wires/81XS650_wiring_(fixed).jpg

I now believe I've tracked it down to that main yellow wire that plugs directly into the headlight. I'm not getting anything close to the 12v I assume I'm supposed to be getting (since the headlight says 12v on it). I tried measuring it with the bike running, and I get the same reading (something very low like 0.04v, but definitely not zero).

If you follow that yellow wire back from the headlight, you can see that it also feeds the high beam warning light (which also happens to not be working for me, though to be honest, I don't remember if it ever worked before). If you keep following this wire to the right on the diagram, it looks like it comes from the "reserve battery unit." According to a google search, this thing is supposed to keep the headlight from turning on until the engine is running, but that makes me think I don't have one. I know for sure that my headlight used to turn on whether the bike was running or not.

So now I'm a little lost on what to check next. Any tips? Does it sound like I'm on the right track? Just to summarize, the only lights that aren't working are my headlight and my high beam warning light. Everything else seems fine.

It might be your switch on your handlebars. There are moving parts in there and they corrode over time. Get some electrical contact cleaner, open up the housing and spray the contacts, move the switch, and repeat. Might be all you need to do.

Ah, I thought of that too. I actually bought a brand new bar switch assembly and installed it today. It didn't help though. That's when I discovered the issue with that main yellow wire.

11.4 is a low battery reading, if the bike is charging the battery should be showing above 12 volts with the bike off. Oddly if you have stock wiring the XS headlight will not light unless the alternator is working. That reserve lighting device can be a trouble maker also.

Read this thread for suggestions on how to check/bypass the reserve lighting unit.

I had issues here. My wiring harness was loose. Took it all apart & cleanly put wires, tie straps etc back together. Could be the ground. Some bars need scraped possibly where the switch grounds under the controls. Scrape contact area. Good luck. Was there too.

Had a similar problem a few years ago. One of the wires to the 3-prong headlight connector had a hidden break near the connector where the wires try to bend around the connector, caused by folding back during headlight install...

The yellow wire that goes too the headlight is the high beam feed. It should get power when the dimmer switch is in high beam position.
The green is power too the headlight in low beam position.
The black is ground.
When you are tracing power start on the battery side of a circuit and go along the circuit to find where the power gets lost.
Leo

The saga continues...

I went out and bought a brand new battery this weekend, but it didn't help. Not that I really expected it to, but I definitely needed one anyway.

Next I went around and cleaned every harness and connector I could find. I also replaced a few connectors that seemed loose or questionable. I still have the same problem, but I think I may be a little closer now...

First a picture showing what happens when I put my micrometer on that yellow wire (high beam?) and ground. I get zero volts (or more accurately, 0.04v). This seems very odd. Just for the hell of it, I attached the yellow and black wires directly to the headlight, and unsurprisingly, I get nothing...



Now here's where things get interesting. That yellow wire comes out of a harness that comes from the tach. If I unplug the harness and test the blue wire that feeds it, I get something much more reasonable (just over 11v).



When I attach this blue wire and ground to my headlight, it works!

So from what I can tell, this blue wire feeds into the tach, and the yellow wire comes back down from the tach into the headlight. Since I never see anything but 0.04v coming out of the tach (even when testing it above the harness), am I to believe that something is broken inside my tach? Note that my handlebar high beam switch is totally removed from the equation at the moment.

Hmm, maybe I was wrong about that yellow wire going into the tach. Judging by this wiring diagram, the tach expects to receive current from that yellow wire, so it can light up the high beam indicator appropriately.



But then where does the current originate? Every other loose wire I see comes from the handlebar switch. I must be missing something...

Ah ha! I just found a broken blue wire, barely inside the headlight assembly, that also tests just above 11v. I'm guessing this is the source that feeds the handle bar switch, as this would explain the other broken blue wire attached to my handlebar switch. I don't know why I didn't notice these earlier. Stand by...

YES that tach connector yellow wire is the FEED to the high beam indicator in the tach, it does not supply power to the high beam. I don't know what year bike you have, adding that info to your signature helps us help you.
Here's an 82 diagram, looks like you have a late model special.

View attachment 22987

The late model Xs has a trouble prone headlight module that provides auto switching in the event of bulb filament failure. I leave em in if they work but many just get rid of them, there's a how to. Also the headlight is powered by a latching relay that only latches once the alternator has fed power to it, so the headlight will not light when the ignition switch is turned on but the engine has not been started. The power for the headlight comes from yellow (high beam ) and green (low beam) wire in the main harness bundle in the headlight shell. Confirm you have all the black grounds properly connected as well.

this thread in the tech section has the diagram for every year, look down a few posts. Printing out the diagram is a good idea when chasing electrical gremlins. I have a large diagram hanging on my shop wall.

RLU is under the gas tank in 82 (I think) unplug RLU, jump blue/black to blue/yellow in the connector.

All fixed! Thanks, guys!

On this topic (kinda), does anyone know if I there are any issues by not connecting the headlamp warning indicator (meaning I don't have a bulb connected as I'm using an after market gauge cluster)?

Basically does having the bulb close a specific circuit or restrict headlight or charging functionality?

Thanks in advance!

No. It is used by the RLU as an on dash warning that the headlight has a blown low beam.
So leaving it out won't cause any issues.
Leo

Great, thanks XSLeo!