Hello all,

I'd like to pick your collective brains if I may.

I have a major issue with my 2002 A3 1.9 TDi

My battery is draining overnight. The battery is good (12V on the kitchen work top after re charge), and it is charging when the engine is running (14V when back in situ with the engine idling).

I've measured the current being drawn when everything is off (including interior lights/boot lights etc) and the car is drawing 300mA. Is this anywhere near normal? Would it be enough to drain a battery over 12 - 15 hours?

I then went through pulling and replacing each fuse in turn to see what happened to the current draw.

When I pulled fuse 11 - Instrument cluster, automatic gearbox (it's a manual) the current drawn dropped to 40 mA.

Pulling fuse 38 - Luggage compartment light, central locking sys resulted in an open circuit indication on the multi meter. Does that sound right?

I then had a few further developments.

I have since found out from she who must be obeyed (for tis her car), that a couple of warning lights have been flashing on the car, and the brake lights have been a bit intermittant. (You could of told me earlier love).

The error code reader do da thingymebob gave me just the one code of 16955. I've had a bit of a root around the brake pedal switch and the rear light clusters, and I found this:

(Apologies for the blurryness)



The snakes wedding appears to be an aftermarket alarm sounder. I may be wrong, I know very little about auto electrics. The wires coming out of the tail light cluster have been spliced with other wires going into the various little boxes and bits and bobs, one of which is a relay. I know that because it says "Relay" on it rather than any electrical knowledge on my part.

Anyhow, my digit is pointing to a relatively thick green wire which shoots off into the trim. Tracing the wire forward, it emerges in the engine bay here. I've never noticed it before as it was down behind the battery holder box.




This is where I get very stuck. I have no idea how the electrics work, but a good eyeballing appeared to reveal that the wire was connected to the negative terminal, but whatever was used to secure it to the terminal has come off and so therefore, has the wire.

In close (ish) up:



That stud is quite clean, suggesting there was something screwed down onto it recently.

My next question is, could that disconnected wire be causing my battery drain and brake light issue? And, why run a wire back to the negative side of the battery.....surely, it could use any other earth point around the car?

Thanks for any help...........!!

 

Hello again. I know it's poor form to reply to one's own posts, but I have made some progress, and thought an update was in order for those who may have had a similar issue.

The extra gubbins tucked away behind the rear light cluster was in fact relays and an audible alarm for a towing hitch. A relay was used to power the fridge in a caravan from the car when in use, and switch back to the caravan's leaisure battery when the car was off. The second relay was for the lights, stop lights and turn signals on the caravan. The audible alarm is to satisfy a legal requirement in the UK that the indicators on a towed vehicle have an audible tone to signify they are connected and working.

I have cut all the rubbish out that isn't required and terminated/insulated correctly the stock wiring. i still have an issue with the brake lights doing their own thing when they feel like it. I have ordered a replacement brake light switch which after reading all the forums will hopefully cure my woes.

I think that some of the DIY wiring was "a little dodgy" which may explain the draining battery. I also didn't realise that the brake lights work without the key in the ignition. It's entirely possible that the brake lights have been on after I have left the car, which would also drain the battery fairly rapidly I'd imagine.