High beam indicator stuck on, headlight flickers

Hello again!

Ran into an electrical issue today on my '81 XJ650 Maxim. On the way home from work, I noticed that the high beam indicator lamp was flashing whenever the engine was revving. I thought that was the only issue, but once it got darker, I also noticed that the light itself was dim and flickering while the indicator lamp was flashing. All of these issues went away when the engine dropped down to idle.

It seems like there must be a loose connection somewhere in the circuit. My guess is the engine vibrations are causing something to come loose. I pulled the headlight off tonight and checked the connectors on the headlight itself. Everything looked clean, and I sprayed some contact cleaner in the female ends just in case. Unfortunately, it had no effect.

Any idea what could be the issue here? Fusebox, perhaps? I could see a bad fuse connection messing with the headlight, but I don't know how that would explain the effect on the high beam lamp.

 

Guess the switch might be the issue. I know that many of my re-fresh jobs I have had the solder connector from the right and left side bar switches come lose. Not much room in there, so if that is the case, could be causing a short.
456694312_1621006548513651_3233158243744644067_n by Tim Brown, on Flickr
That is off a Kaw gps550 starter button, but I just wanted to show you that sometimes them little solder joints come lose and you have to re-solder them back on. Good luck with the troubleshooting.

 

Well, what a surprise. I checked the grounds, everything looked good (no loose bolts and no obvious corrosion). I cleaned some more connectors on the headlight circuit. No effect.

Then I decided to check the resistance across my fuses. Bike off, no measurable resistance. Bike on and around 2K RPM, suddenly there’s 500kOhms across the headlight fuse. No resistance still across the others. I tried to clean the clips holding the fuse in, and one immediately snapped.

So it may have been the fuse box all along! Will be replacing that, will update after completing that maintenance.

 

I have an update. Got the new fuse box from Len, and I installed it today. To my surprise, the headlight issue was not fixed. I did see an immediate improvement to the ignition circuit. Previously, the bike was always a little slow to start. It would fire up right away, but even on max choke, the engine would slow down until almost dying, then gradually ramp up to normal idling. This would all take place over the course of just a few seconds, but it was noticeable. Now, that behavior is completely gone. Starts immediately and stays started.

So, having already checked most of the connections in the headlight circuit, I tried something different. I replaced the headlamp. And what do you know… problem solved. No idea what could be wrong with the old one that could cause it to flicker at high RPMs, but apparently it’s something that can happen.

 

I've seen that happen before. Usually, a broken filament in the bulb, but it's still close enough to touch and make a connection when undisturbed. Then strong vibrations can jiggle it enough to break continuity until it springs back into place. Eventually it will probably fail completely.

Don't you hate it when you find the simple fix after you spend all the time on money trying the complicated fixes?

 

It may not have been the root cause but you certainly found issues with it; issues that could have caused a motor to shut off on a freeway or a headlight to go black on a country road, so good fix and something everyone should do.

 

Exactly. Was still a good idea to replace the fuse box, but I could have been riding again sooner if I just tried a new headlight first. It was low on my troubleshooting list because I already replaced it this year. The bike came to me with its original incandescent bulb from 1981, still working somehow. I put in a halogen so that I could actually see at night, but I guess the new bulb was not built to the same QC standards.

 

Too right. The change in the ignition behavior was eye-opening after I made the swap. I could have easily been left stranded at any time, if that connection ever gave out completely.