Fuse 4 keeps blowing

[E34-520iSE]

Hi guys - can anyone help with this one? Fuse 4 (7.5A) has decided to pop, regardless whether the lights are on or off. I have already checked the l/h front and rear lamp connectors, and even unplugged the light switch, in case there was a problem inside it. I studied the wiring diagram and can only assume that F4 is feeding something else, which isn't documented. The problem is somewhere between F4 itself and the light switch - are there any factory splices on that RT/GR feed?

Any help greatfully taken!

Shaun M

[whiskychaser]

If you are looking at the Bentleys diagram its not too clear - it shows fuse 4 as only covering the left side of the car. (It also shows side markers which we dont have)
But under the list for fuse 4 it says it covers:
Side lights including the one under the bonnet
Lamp monitor
Power mirrors
Headlight washer (Canada) - doubt that applies;)
Central body electronics (ZKE)
Any chance an elec mirror button is stuck in?

[E34-520iSE]

Hi Whiskychaser, Yes I checked the power mirror circuit and they are working 100%, even without fuse 4. Any ideas?

Regards,

Shaun m

[whiskychaser]

Hi Whiskychaser, Yes I checked the power mirror circuit and they are working 100%, even without fuse 4. Any ideas?

Regards,

Shaun m
I'm guessing it doesnt blow the fuse straight away or you would have found the short? Sounds like the book isnt too much help. Tried turning the switches on in turn until it blows? ie turn on side lights, then hazards, then brake lights, fogs etc

[E34-520iSE]

I'm guessing it doesnt blow the fuse straight away or you would have found the short? Sounds like the book isnt too much help. Tried turning the switches on in turn until it blows? ie turn on side lights, then hazards, then brake lights, fogs etc

Nah, the fuse blows immediately on being plugged in, so I am driving about with no fuse 4 in at the minute, otherwise I would have done the 'switch on everything til it blows' routine as you describe. Strange one eh?

Regards,

Shaun M

[whiskychaser]

Nah, the fuse blows immediately on being plugged in, so I am driving about with no fuse 4 in at the minute, otherwise I would have done the 'switch on everything til it blows' routine as you describe. Strange one eh?

Regards,

Shaun M
Handy till it gets dark:D As the lighting switch is on the live side, you have to conclude there is a dead short between the fuse and the switch somewhere. I couldnt find a likely spot in the diagrams. Apart from pulling the LKM and seeing if the fuse still blows, I think you are saddled with a bit of a search

[Bo525i]

I attached fuse 4 charts from a 1990 and a 1992 for reference and diagnosis search!

[Bo525i]

1990

[Bo525i]

1992

[E34-520iSE]

Thanks for the help Whiskychaser and Bo525i.I've drawn a blank - looks like I'm getting a replacement 535 loom sent to me, which is good news anyway as then I'll have a complete check control set-up and ABS - Onwards and upwards lol!

Regards,

Shaun M

[Ross]

I think there is a parking light relay also on fuse 4.
Too bad E34s don't use the tubular glass fuses, Ive heard a .22 cal rifle bullet will fit.

[whiskychaser]

I think there is a parking light relay also on fuse 4.
Too bad E34s don't use the tubular glass fuses, Ive heard a .22 cal rifle bullet will fit.
I dont think our side lights have a relay Ross. You mean insert a live round then reconnect the battery? :D

[Ross]

I dont think our side lights have a relay Ross. You mean insert a live round then reconnect the battery? :D

Someone famously did just that according to the legend. In an older American pick-up truck that had it's fuse box positioned just at the bottom edge of the dashboard with the fuses oriented longitudinally. As the story goes it took a while for the "fuse" to heat up sufficiently to,...you know. Given the positioning of the fuse it's not hard to guess the trajectory. 'Ol Billy Bob sings soprano now.