Number 10 fuse keeps blowing

Tue May 17, 2011 12:08 pm

A while back I was driving along when all the dials stopped working (except speedo). When I turned the engine off it wouldn't re-start (not even turn over). I had a quick check of the fuses and they looked ok, so I thought it must be the ignition switch. I fitted a new BMW ignition switch but that didn't solve the problem, so went and re-checked the fuses more carefully and found number 10 fuse had blown (yes I am an idiot). Replaced the fuse and the ignition came on ok and dials worked etc. However just as I went to start it, the fuse blew and it wouldn't start. I tried fitting a bigger current fuse but the same thing happened. Ignition switches on for a couple of seconds then the fuse blows.

Has anyone encountered this before? I'm guessing its an electrical short somewhere, but don't have the time atm to take the dash out and check all the wiring.

From what I can tell number 10 fuse controls:
- signal to starter motor
- some of the ignition warning lights
- dials (except speedo)
- check panel
- interior fan
- electric mirrors

Any suggestions?

Tue May 17, 2011 12:13 pm

Fuse 10 also operates the reversing lights...

I would have the decorative gaiter around the gearlever up and un-plug the wire that comes up from the reverse light switch first....

The part of the harness that runs to the gearbox switch can rub on the propshaft,causing it to short and blow the fuse.

Tue May 17, 2011 12:30 pm

something is shorting it out, check the obvious things first.

Tue May 17, 2011 1:10 pm

daimlerman wrote:Fuse 10 also operates the reversing lights...

I would have the decorative gaiter around the gearlever up and un-plug the wire that comes up from the reverse light switch first....

The part of the harness that runs to the gearbox switch can rub on the propshaft,causing it to short and blow the fuse.

You might be onto something there. The reverse lights don't work atm. The wires to the reverse light switch frayed through a while ago, so I soldered in a new section and the reverse lights worked for a bit, but then stopped working again. As it doesn't cause me any inconvenience having no reverse lights, I hadn't bothered to fix it again, but if they use number 10 fuse then thats a likely cause.

If you ask me its not a very clever place to run a wire, right next to the exhaust and the prop shaft.

Thanks for the tip, I shall check what state that wire is in.

Tue May 17, 2011 1:24 pm

No need really just disconnect the block under the gaiter and see if the problem goes away

Tue May 17, 2011 1:30 pm

The harness should be clipped to the gearlever mounting plate.....

If you un-plug the harness leading down to the switch,join the pins on the car side of the harness,with the ign on the reverse lights should work,this proves the rest of the circuit.So fuse 10 blowing is either the wire catching and wearing through(shorting to earth)or a faulty reverse light switch...

But if you still have problems with the reverse light switch un-plugged then we need to look further...

Tue May 17, 2011 5:43 pm

I had exactly the same problem with my car when I first did my m50 build !!
Drove it around for a bit before I lost all instruments (except speedo), fuse 10 being the culprit and as daimlerman said above it was ideed the reverse light wire had chaffed on the prop centre doughnut! Put a spare 1 on there and cable tied the bitch up nice and covered 5000 trouble free miles