High beam blowing fuse every time.

gjws · Jun 17, 2013

Hi all,

Electrical problems with my 2012 FE390.

I've recently done some electrical work and now every time I switch on the high beams the fuse blows, low beam works just fine. I've only made some very minor tweaks to pickup power for a Trail Tech Vapor and Montana GPS cradle, which I have tapped in to the S7, the connector for the starter switch, however I've obviously crushed a wire somewhere along the line.

Looking at the wiring diagram S5 is the switch that controls the lights, and it appears that there are 6 wires that make up the combines lights/horn/kill switch. Can anyone possibly shed any light on which wire is for the high beams? I can't make heads or tails of the diagram, there are too many wires, but I'm guessing that the high beam wire it hitting ground somewhere and shorting every time I turn it on.

Thanks!

gjws · Jun 18, 2013

Update:

So there are 6 wires that head up to the light/horn/kill multi switch:

White
Brown
Gray
Blue
Yellow
Green

White is switched on whenever the lights are on, either low or high, it turns on the rear parking light.
Brown brings a negative to the switch for the horn.
Gray takes the above negative out to the horn.
Blue is a negative leading to the high beam.
Yellow is a hard active from fuse 3. This is the fuse that keeps blowing.
Green is a negative to the low beam.

When I hit the switch for high beam the light comes on for around half a second, then the fuse blows. But I'm terribly confused with the way auto electricals work. Normally in a house you have a negative (neutral) as the light and take a positive (active) to the switch. In auto, it appears you leave a positive at the light, and take a negative to the switch, does that sound right? So I figure there must me a short on the blue wire, but it doesn't appear so. I HATE AUTO ELECTRICS!!!!

I'm going to keep testing but any suggestions are most welcome.

jimmythehat · Jun 19, 2013

autos almost all negatively earthed. I.e. + switch - application - earth. you need to remove bulb, then test for resistance from negative side of switch to frame (earth) you get a reading I think you are shorting. most likely in the light fitting itself.

gjws · Jun 20, 2013

jimmythehat said:
autos almost all negatively earthed. I.e. + switch - application - earth. you need to remove bulb, then test for resistance from negative side of switch to frame (earth) you get a reading I think you are shorting. most likely in the light fitting itself.

Thanks Jimmy. I have been pulling my hair out here, must have give through 20 fuses so far in testing so I finally went and purchased some blade fuse circuit breakers. Great item, slots straight in place of the standard fuse and when the circuit trips you just press a button and reset it. Unfortunately they are too big to leave in permanently, but useful for testing.

Only problem was......IT DIDN'T TRIP!!! That drove me nuts so I pulled the fuse out and placed a multimeter across the fuse point. Low beam was pulling ~2.5 Amps but high is pulling 15 Amps! Great, thanks circuit breaker!!

So definitely looks like a semi-short and agree it looks to be in the fitting as it isn't a direct short to earth. I tested resistance of the globe and from both the green and blue side I get amount 0.2 ohms from memory, could be wrong as it was a couple of days ago but point is I was seeing pretty much the same resistance on both high and low which I thought was weird. Think ill get a new bulb and try again, even if its not the globe it's nice to have a spare in the toolbox.

09berg · Jun 20, 2013

My high beam blew the fuse every time for a while. It boiled down to be the low fuel indicator wiring that I had not been using was the cause of the short. Do you a have a low fuel light installed?

gjws · Jun 20, 2013

09berg said:
My high beam blew the fuse every time for a while. It boiled down to be the low fuel indicator wiring that I had not been using was the cause of the short. Do you a low fuel light installed?

I do have it installed, it seems to be working OK but auto elec wiring is the most bizarre thing I'm always amazed how something seemingly unrelated can be the cause of a problem!

The wiring loom was crushed against the frame bracket for my Scott damper for a couple of weeks before I pulled the loom bracket off whilst installing the Vapor, I hadn't noticed after installing the damper as I never looked at the wiring. I thought I'd fixed everything, and I certainly can't see anything that is exposed but I'm obviously missing something.

There is the old cabling that went to the stock computer not in use since I installed the Vapor, I've not looked at that so it's a good place to check. Thanks 09berg.

Galbo950 · Jun 22, 2013

I picked up an 09 570 Berg on Thursday and it had a similar issue. When I first got it I had no lights working, traced it back to a faulty headlight switch, that got me the park light, low beam and tail light working, but every time I tried high beam the fuse would blow. Worked out that the cause for the fuse blowing was actually the high beam indicator light fitting on the dash that was shorted. It was the actual fitting that was shorting out, the fitting had no bulb in it resulting in the 2 terminals touching each other. I gave it a good clean out and reshaped it so they wouldn't short out anymore and then put a bulb (1.2watt) in, haven't blown a fuse since.

Rensho · Jun 22, 2013

See if you can measure draw between the switch and the wire leaving the switch for highbeam. This will tell you if the short is before or after the switch.
Also, see if High works fine without putting the mask back on fully, as that always smashes a bunch of wires, specifically the headlight wires.

gjws · Jun 23, 2013

Thanks very much guys, all the suggestions were a great help and I found the problem!

It was the switch, well it was the wiring loom to the switch. The light switch was pushed up hard against the clutch lever, and the cable had been routed between the two. Given that the bike is only 3 months old I was shocked how quickly it had worn through, and the blue cable running to the high beams was just touching the frame. Not enough to provide a direct short, but enough to blow the fuse after a second or two.

If anything good has come of this, I now know my electrics intimately so feel much more comfortable working on the bike!

High beam blowing fuse every time.

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