Headlamp fuse blows when I switch to high beams

Ok, I actually think I fixed this one by myself for once without asking someone on this forum for help. :blush:

I still thought I'd pass along the info in case it helps another noob.

I was driving home one night a week or so back, flicked on the high beam and my lights went out. Turned out I had a blown fuse. Replaced it everything seemed fine, including the high beams. A few days later it happened again and I knew I had a problem.

After about the third fuse it started blowing them every time I switched on the high beam instead of intermittently.

I took apart the high/low beam switch and didn't find any shorts. I started going through the connectors in the headlamp bucket, taking each connector apart, cleaning them, making sure they were tight. Everything seemed pretty clean though.

I continued going through connectors paying particular attention to anything in the headlamp circuit on my wiring diagram but also checking anything else I found along the way. I found very little corrosion or loose wiring. The previous owner must have done this before me.

Once I'd gone through every connection I could find that seemed related to the headlamp I put a new fuse in tried the high beam and blew another fuse.

I looked at the wiring diagram again and found a ground connection I'd missed in the headlamp circuit. It was back by the battery and sure enough, loose and a little corroded.

Cleaned, tightened and my high beam works beautifully again.

Bad connection/corroded connection can not blow a fuse 0.0000% chance as it's not electrically possible. Only exception is bad connection right at the fuse clips which causes fuse to overheat and burn.

what if there is a broken wire and everytime he hits the hi-beam switch it grounds out on the handlebars?

RonKZ650 wrote: Bad connection/corroded connection can not blow a fuse 0.0000% chance as it's not electrically possible. Only exception is bad connection right at the fuse clips which causes fuse to overheat and burn.

Hmmm... just when I think I know what I'm doing....

Well at that same connector there was a small spot where the plastic around the base of the clip was worn and a bit of the metal was showing. I wrapped a little electrical tape around it at the same time I cleaned and tightened the connection.

I didn't bother mentioning it because it didn't look like it was touching anything. Even if it was, this is clearly a ground wire. Would it blow a fuse if it grounded to the frame?

I'm at a loss here. My high beam is working again. But I don't know what I did to fix it.

Topper, if the high beam is the only cause, the low beam works fine, then the short has to be on the high beam wire from the handlebar switch out to the bucket/ bulb. This is the voltage wire, and not ground. If your wires go Through the bars, then this is the most likely area where the insulation is damaged.

Topper wrote: Hmmm... just when I think I know what I'm doing....

Well at that same connector there was a small spot where the plastic around the base of the clip was worn and a bit of the metal was showing. I wrapped a little electrical tape around it at the same time I cleaned and tightened the connection.

I didn't bother mentioning it because it didn't look like it was touching anything. Even if it was, this is clearly a ground wire. Would it blow a fuse if it grounded to the frame?

I'm at a loss here. My high beam is working again. But I don't know what I did to fix it.

It wouldn't matter if only a ground wire (usually black/yellow) is "shorting" against the frame or other grounding site.

A fuse typically blows when a "hot" wire is shorting (grounding) against the frame or other grounding site.

Where a hot wire continuously vibrates against a ground wire, the wire sheaths may eventually wear enough at the point of contact to expose the inner wires to each other, resulting in a short that blows the fuse.

Sometimes a potential wiring trouble spot is avoided (perhaps inadvertently) by slightly moving the wires around, inside the headlight for instance.

Good Fortune!

Patton wrote:
Sometimes a potential wiring trouble spot is avoided (perhaps inadvertently) by slightly moving the wires around, inside the headlight for instance.

Good Fortune!

That must be what happened. In the course of going through the wiring I must have reajusted the wires and somehow stopped the short from happening.

I'm still pretty confused though because I tried replacing the fuse and testing the high beams a couple times along the way. It wasn't until I messed with this loose black/yellow connector by the battery that the high beams started working normally.

Motor Head wrote: Topper, if the high beam is the only cause, the low beam works fine, then the short has to be on the high beam wire from the handlebar switch out to the bucket/ bulb. This is the voltage wire, and not ground. If your wires go Through the bars, then this is the most likely area where the insulation is damaged.

The wires don't go through the bars, but they're bundled up in the harness pretty quickly within a couple inches of leaving the switch housing.

My high beam lead is red/yellow and goes from the switch housing to a 6P connector then into the headlight bucket. I inspected all of it I could see. Maybe there's a short inside the harness somewhere and I just got luck in moving everything around.

Well, its fixed for now and I still learned something even if it wasn't what I thought I was learning at the time.

Thanks as always for all the help.