light fuse popping

[Phil_G]

Hiya,

My 2001 M49 has developed a slight irritation in so much as it blows the 5a fuse that covers the Near side rear tail light and Driver's side front side light. Is this a common issue with a bad earth or am I going to have to throw some money at it with an auto electrician and get it sorted that way?

Regards,

Phil

[Phil_G]

Update - When i press the brake pedal and illuminate the brake lights, the reverse light illuminates too...

[lorraine]

bad earth!

[Phil_G]

only does it when pressing brake pedal. I.e it will light the reverse and tail lights. It will not light the tail lights when selecting reverse but does light the reverse lights (if that makes sense). I.e It's a one way street and surely that fault would manifest itself either way given that the earthing point is common on each side if that was the case and/or affect other lights on the side which are fine. The earth has literally zero resistance from the bulb holder to the earthing point behind each light so I'd assume that (at this time) to be ok but I'm light limited now and will carry on investigations tomorrow when I have more light.

edit to add; overlooked obvious. It may be there is a relay that fires the brake lights so yes, it could be an earth and that could be why it doesnt "go both ways". Can anyone with a Haynes manual confirm this please? It's a 2001 1.9D 800. Thanks

[Ol'Jeffers]

The part of all this that bothers me is the fuse that keeps on blowing. I don't think it's related
to the reverse/brake light fault unless there's damaged wiring somewhere in the relevant harness/loom.
A poor earth isn't likely to cause that to happen but water ingress into the bulb holder might.
I would be removing the rear light units and checking for chafed cables. Operating the brake pedal with one then the other
brake light bulbs removed. If you remove both brake light bulbs does the reversing light still come on?
The brake lights are not likely to have a bespoke relay.
Hope this gives you an idea of more you can check.....let us know the outcome!!

[BlueBlingo]

Ol jeffers has a good point !

It sounds like you have a chaffed wires in harness to rear lights !
So your 5 amp fuse is trying to supply an over rated load (more bulbs than normal)

Brake light is not fed thru a relay !

Is there a toe bar + additional wiring for it Fitted ?

[Phil_G]

Hi,

No tow bar and more oddness. When I put it in reverse or brake, the O/S/F side light illuminates. The only non factory wiring in the back relates to a reverse alarm thingy that has been unplugged but the wiring left in place. I will remove it properly tomorrow and see if that helps otherwise wiring (to my best knowledge) is factory, although it's an excellent point you've raised.

Still puzzled as to why only the one fuse pops but I'll get to the bottom of it.

thanks both for your help

[Ol'Jeffers]

May be a good idea to have the BSI checked as that procedure will also highlight
a wiring problem. Just a thought. (Does the Mk1 have a BSI??) Does anything specific have to be done
to blow the fuse or does it happen arbitrarily?

[BlueBlingo]

Brake light supply does not go thru BSI
When you put it in reverse or brake does the NSR running light illuminate ?

If you are still having problems can you provide as much vehicle info as possible & I will try and sort out wiring diagrams + info for you:
Engine type
Transmission type
Side door
Rear doors or tailgate
LH or RH Drive

Can you also provide your RPO Number if possible its usually a five digit number on a sticker Below the driver side `A` post it should be between 08610 and 09184.

[Phil_G]

Hi,

I've gone as far as I'm confident to go now as whatever is wrong would appear to not be a simple cleaning of a contact so I've called a pal in who's an auto electrician (and a good one at that). I will let everyone know what's found

thanks

Phil