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 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