Here,s one for the budding auto electricians

[beast5680]

My 300tdi ES auto 98my has a curious electrical fault thats started today :roll: when you apply the brakes the rear window demist light on the demist switch comes on, with no brakes on everything works as normal, now i suspect a chaffed wire somewhere feeding the switch but having been out to drop off daughter i stopped at her friends went to switch off the engine and it wouldnt turn off :shock: and the check engine light was glowing dimly, reinserting the key and switching it back to on i removed my foot from the brake and switched off as normal, are there any common chafe points i should be looking at?
the fault only seems to occur when the brake pedal is pressed and i cant get it to replicate the not switching the engine off part.

any suggestions welcome

[beast5680]

well having had a dig round in the dash i,m sure the brake light wire must be shorting across to the rear heated windscreen wire, having removed the relay,fuse and switch for the rear screen it still gets live from the brake :-. does anyone know where the loom runs front to back in a disco?

[GREENI]

Cut a small piece of electrical tape...black works best, and put it over your rear window demist light...VOILA 

[beast5680]

Cut a small piece of electrical tape...black works best, and put it over your rear window demist light...VOILA 

cheers for that but.....already done :lol:

[bobthedisco]

well having had a dig round in the dash i,m sure the brake light wire must be shorting across to the rear heated windscreen wire, having removed the relay,fuse and switch for the rear screen it still gets live from the brake :-. does anyone know where the loom runs front to back in a disco?

Hi, the loom that runs front to rear is up the n/s front pillar then along the roof and drops back down the n/s rear pillar :)

[Disco_Stu]

Do the rear screen de-mist and the brake lights/rear lights share an earth at the back of the car anywhere? More a guess than a suggestion I'm afraid.

[peasey]

I would be looking at the wires as they come out of the body and go into the rear door(the one that the spare bolts to)if you look to the right when its open you will see a black rubber tube thingy pull it out and have a look in there,theres loads of wires there and lots of sharp corners to chaff upon my rear loom was a real mess in exactly that department worth a try mate.

[beast5680]

well after pulling the car to bits today and tracing the wires i,ve found the fault :roll: some weeks ago i replaced both the rear door hinges, unbeknown to me the wires for the rear demist and the high level brake light run right next to the upper door hinge and i didnt see them when fitting the hinge and managed to trap them together between the hinge and the door when i bolted it in :doh: although not earthing they had become joined hence the rear demist coming on when the brake was applied,
will learn from that mistake :doh:

[lurch_917]

allso check the chassis earths as thes are prone to dirt and crap getting to them

[Disco_Stu]

Do the rear screen de-mist and the brake lights/rear lights share an earth at the back of the car anywhere? More a guess than a suggestion I'm afraid.

I was right!! But in a completetly unitended kind of way :) :)