Rear wiper & window demister problems

[Ian Simmonds]

Over the summer I've been noticing that whenever The rear wiper operates the rear heated screen switch would 'flick on' for a second... Anyway, with the frost this morning I now realise the heated screen didn't work, full stop.

So tonight I checked the fuse (No 16 - 30A) and its blown, so fitted a new one, turned on the rear screen demister and not only did it work, so did the rear wiper motor, constantly...

Any thoughts as to how and where they are sharing feeds?

Many thanks in advance.
Ian

[Nuvo]

First port of call would be to check the condition of the loom in the hinged area of the tailgate. I would expect to see some shorted wires here.

[Error404]

yup, they probably have a shared earth down there somewhere, maybe its shorting them both

[benntenn67]

yes ^^... and another, the loom - body to tailgate, flexing of the wires opening & closing the tailgate over the years fatigues them

[Ian Simmonds]

Thanks folk... I'll have a mooch...

[macspring]

First port of call would be to check the condition of the loom in the hinged area of the tailgate. I would expect to see some shorted wires here.

Agreed, same as B4 Cabrio boot looms, and Avant tailgate looms.

More obvious these days, but it is apparent that these parts of the respective looms were not designed to last as long as the rest of the car has.

[Fat Audi 80]

My coupe was a nightmare in flexible connection. Once you get the rubber boot off you will see the black sticky wiring loom tape. Even if it looks perfectly intact, don't be fooled! Mine look perfect and I was reluctant to strip it back. Once I did however, the coloured insulation had cracked on ALL the individual wires. I sourced the correct colour insulating tape (in most cases) covered them and put new loom insulation over it all.

Heated rear window, wiper etc worked properly again without blowing fuses....

Good luck.

Cheers,

Steve

[Ian Simmonds]

My coupe was a nightmare in flexible connection. Once you get the rubber boot off you will see the black sticky wiring loom tape. Even if it looks perfectly intact, don't be fooled! Mine look perfect and I was reluctant to strip it back. Once I did however, the coloured insulation had cracked on ALL the individual wires. I sourced the correct colour insulating tape (in most cases) covered them and put new loom insulation over it all.

Heated rear window, wiper etc worked properly again without blowing fuses....

Good luck.

Cheers,

Steve

Steve, you really don't know how timely that post is... I got home from work about half an hour ago and pulled the wiring boot off only to reveal the black inner sleave... So was going to ask, do I cut the sleave and boot?

I'm off work from Thursday next week, so I think I'll wait until then... And do it properly without rushing...

Also any idea which side rear screen demister and wiper pass through, there are boots on both sides...

Kind regards
Ian

[Fat Audi 80]

Hi Ian,

I don't know which side it is, there is only one rubber boot on the Coupe. I would add some wd40 or similar to allow the boot to "slip" off. I then cut one part of the black loom felt and unwound it. You should find the culprit after that.

Cheers,

Steve

[Ian Simmonds]

I've dismantled the wiring today, and bloomin'heck, it was well and truly gone...





So I've lovingly soldered them all back together and individually insulated them, and now I've got another problem. The headed rear screen works fine, but the rear wiper won't 'go', the screen wash is okay. Fuses are all good, and the wiring was definitely soldered up in the right order.

Any thoughts?
kind regards
Ian

PS - For reference, its the passenger side.

[Donnie]

There is a relay under the seat, this same thing happened to my avant. I had no rear wiper unless I used the wash, the demister used to fuse regularly too. Once I stripped back the insulation it looked like your photos - amazing that anything worked at all. Anyway the relay under the seat must have been damaged by the shorting, I borrowed one and all was well except the owner of the borrowed relay wanted it back.