headlight fuse keeps blowing

[brucealmighty]

On an average of once a week, I'm replacing a blown headlight fuse. I did away with the original buss type fuses and replaced them with blade fuses, hoping that might solve the problem, but nope. I'm wondering what is the purpose of the "reserve lighting unit". I thought that was supposed to keep the lights on if the main circuit failed. Also, the "headlamp" warning light on the dash doesn't come on. Any thoughts on this?

[DiverRay]

Need a little history on your bike. I WOULD start looking inside the headlamp bucket, and check all the wire bundles that feed through the back of it. If you have a special, the metal edges could have worn through the wires, and be causing a "short" at some combination of turning and bump. That would be my first guess. Next would be too look at ALL the connections, both hot and ground, and CLEAN everything up, put on dielectric grease, and see if that helps.

[brucealmighty]

It's a 1982 XJ1100. I guess I don't understand a lot about electrical theory. It seems to me that the fuse blows because there is a short somewhere, not surprising on a 25 year old bike. But, if there's a shorted connection, why does a fuse last a week before blowing again? Is it maybe a matter of the bike getting bumped just the right way to make the connection happen, but then goes back to normal?

[DiverRay]

After 25 years, some of the wires may be rubbing on the headlight bucket, or any other spot near the front end. The fuse may be able to hold a mild short, but blows when things get in just the correct place. Think of it as a leaky water pipe. find and fix the leak, and no blown fuse. You could try putting electrical tape over each of the wire bundles that come through the frame and into the headlamp bucket. If that lets the fuse last longer, you know the location of the short. To just do a visual, check all the wire bundles going in, and look for someplace that a wire has been rubbing. Don't forget to check the wires that go to the headlamp bulb itself, as they can be the problem.

[brucealmighty]

Thanks. I've only owned the bike a couple of months and haven't had a chance to do much with it, but then, it hasn't needed much. When I've got a couple of hours, I'll pull the headlight and check the condition of all the wires I can find.

[79XS11F]

I agree with the others ... you have a short somewhere in the system and it is in deed likely in the headlight pod. As for the emergency head reserve devise... It does not guarantee a headlight when the circuit fuse blows. What it does is switch to the high beam filament if the low beam filament blows. I'm not sure if it also does the same thing going the other way from blown high beam to turning on low beam.
Rob

[Shuriken]

I pity you.

Years ago, I had a problem on my XS650 that caused the headlight to blow. After going through like half a dozen headlights and never finding the problem, I got rid of the bike. (I was going to sell it anyway, but the headlight problem sped everything up!) I'd be riding and, pop goes the low beam. Switch to high beam (or the relay did it for me), and pop, there goes the high beam. This was such a problem that I nearly got stranded several times. Not sure what caused this.

I don't have a wiring diagram in front of me at the moment, but it seems like there are more components than just the headlight on the same circuit.

On this (or another, I don't remember) XS of mine, I once had a problem that when I turned on the ignition switch, a fuse blew. Spent hours and hours looking for problems. Tore into the wiring harness. Nothing. Went through so many fuses that it didn't take long for me to go down to the store and buy an automatically-resetting fuse. I installed that and then I was able to do some more troubleshooting.

I even went as far as putting a compass against the harness and checking for strong electromagnetic field changes at the advice of some others. No avail.

Finally, in desperation, I started disconnecting everything. The last thing I disconnected was the horn. Lo and behold, no more "click-goes-the-fuse." The horn was stuck.

You need a good multitester, lots of patience, a wiring diagram, and a systematic way of checking things in order to solve the problem.

Ben

[brucealmighty]

Last year I restored a 1980 Kawi 440. It had been sitting outside for a long time and there were so many shorts in the system because water had gotten into the wiring harness, that I just tore everything out and rewired the entire bike. Having had the experience of doing that, I know there are things I can resort to, if I must. If I am unable to locate the source of this particular short, I will run a new circuit to the headlight, directly from the battery. Then, it doesn't matter what the old circuit does. Of course, you have to have a hi/lo switch, but I could use a two way toggle switch for that. I hope it won't come to that but, we do what we must.

[AlanB]

Hi Guys,

What size (amperage!) of fuse is it blowing?...... Does it have a high-power (100w) bulb fitted?

AlanB

[brucealmighty]

fixed it, thanks!

Originally posted by DiverRay
Need a little history on your bike. I WOULD start looking inside the headlamp bucket, and check all the wire bundles that feed through the back of it. If you have a special, the metal edges could have worn through the wires, and be causing a "short" at some combination of turning and bump. That would be my first guess. Next would be too look at ALL the connections, both hot and ground, and CLEAN everything up, put on dielectric grease, and see if that helps.

I think your first quess was correct. Upon removing the headlight from the bucket and inspecting the wires coming through the opening, sure enough, a green/white wire running directly to the headlight had been rubbing up against the sharp metal edge of the bucket and the insulation was worn to point where I could see bare wire. I wrapped everything up in electrical tape and installed a new fuse. Now we'll see if that solved the problem, but I think it will. Thanks.