Fuse #4 Keeps Blowing

[deadpheasant]

Hi everyone, I'm new to this site so please bear with me. I've recently bought a 1992 E34 520 SE. It's quite a high miler (149,950) but it's in decent nick except I have a problem. During todays crappy weather, my brother noticed that the left (nearside) side light wasn't working. After investigation it seems that both the front and rear sidelights don't work as the result of a blown fuse. After searching in Halfords for some 7.5a fuses, I replaced it only for it to blow again instantly - as soon as the blades connected. I tried it again and the same thing happened. I replaced the bulbs but still no luck. Just wondered if anyone had any ideas as to what could be blowing the fuse?

Thanks in advance

N

[DaveVoorhis]

Just wondered if anyone had any ideas as to what could be blowing the fuse?

The same thing that always consistently blows a fuse -- a short or excessive current draw in the wiring downstream of the fuse. F4 leads directly to the light switch, at least in the wiring diagram I'm referring to, so if the fuse immediately blows even with the switch off, I would suspect the switch itself or the wiring between the fuse and the switch. If it only blows with the switch on, you'll need to check the wiring, LKM, bulb sockets, etc., downstream of the switch.

[deadpheasant]

The same thing that always consistently blows a fuse -- a short or excessive current draw in the wiring downstream of the fuse. F4 leads directly to the light switch, at least in the wiring diagram I'm referring to, so if the fuse immediately blows even with the switch off, I would suspect the switch itself or the wiring between the fuse and the switch. If it only blows with the switch on, you'll need to check the wiring, LKM, bulb sockets, etc., downstream of the switch.

That's great, I'll get the switch out and swap it with another one to see if that works. Thanks for your help.

[DaveVoorhis]

That *might* be it, but you're probably better off getting out the trusty ohmmeter and verifying that really is it.

[deadpheasant]

That *might* be it, but you're probably better off getting out the trusty ohmmeter and verifying that really is it.

I removed the light switch on the dashboard and put a new fuse in slot 4, but still it blew instantly - even though there was no switch there. I'm no auto electrictian, hell, I'm not even an electrician, so I think I'll take it to the people could fix it for me.

Thanks for all your help though.

[DaveVoorhis]

Do you have an aftermarket stereo? If so, I wouldn't be surprised if someone tapped the line from F4 in the dash to run the stereo, power antenna, or suchlike, and bodged the wiring or insulation.

[Bill R.]

parking light relays, a left and a right , up under the dash by the hood release.
The left one is on the fuse 4 circuit and controls the left parking light relay before it even goes to the headlight switch. That relay is K26. I would remove that first and see if your fuse still blows.

I removed the light switch on the dashboard and put a new fuse in slot 4, but still it blew instantly - even though there was no switch there. I'm no auto electrictian, hell, I'm not even an electrician, so I think I'll take it to the people could fix it for me.

Thanks for all your help though.

[deadpheasant]

Do you have an aftermarket stereo? If so, I wouldn't be surprised if someone tapped the line from F4 in the dash to run the stereo, power antenna, or suchlike, and bodged the wiring or insulation.

Hi Dave,

Yes, it does have an aftermarket stereo in there, not fitted by me though, I've not taken it out to see how it's been fitted. It really annoys me when people just don't use the Autoleads type ISO connectors and just hack their way into the loom. I'll get it checked out - I was thinking of changing the stereo anyway - peobably will have to get a pro to fit it now though!

Cheers