Audi S8 D2 electrical problems

[H24K]

I have a 2000 Audi S8 D2 which is a Great car but has a battery drain fault which as of yet has not been diagnosed and basically if i dont drive the car for about a week or so it dies on me and I found that I can use a booster pack or other electrical source through the cigarette lighter to give the car enough power to be able to open the boot and access the battery, my key does not seem to fit in the boot lock so ive had to use this option quiet a few times now,

I borrowed my friends snap on booster pack which is 1700amps i believe, quiet a powerful one, anyway I plugged it onto the cigarette ligther plug and all the lights on dash etc come on, I should have just done what I usually do and press the button to open the boot but I tried to start the car instead and it made those clicking sounds like when the battery is very weak and then all lights went off and nothing would come back on!!

I played with the cigarette lighter connection etc but nothing still so I checked the cigarette lighter fuse praying that it was blown but its not!!! Does anyone have any idea of what could have happened, for the cigarette lighter not to be working anymore could this have burnt out??

Now im completely stuck as I cant open the boot with the key and cant get no power through the cigarette lighter to open it, and am thinking that something else may have blown out due to me trying to start it with the booster pack?? Any advice is Greatly appreciated. Thanks

[RichardW]

The cigarette lighter socket is designed to supply, at most, 10 amps. When starting a car the starter motor requires between 200 and 300 amps. There is no way you can ever start a car through the cigarette lighter, at best you can do a slow trickle charge of the battery. Your normal procedure has worked because the current drain just to open the boot is less than 10 amps. I am surprised that you have not blown the fuse that protects the cigarette lighter circuit. You may have burnt out a wire or blown another fuse. There is a large high capacity fuse that protects the main supply from the car battery this may have blown but I cannot remember where it is (I sold my D2 S8 5 years ago). I am not sure if the rear cigarette lighter is on a different fuse, you could try that. The other way you may be able to provide sufficient power is to connect the positive terminal of your booster to one of the fuses in the fuse box and ground the other end to an earth point on the car. The fuse that protects the central locking system might be a good one to try.

Be thankful that you do not have a D3 A8. You would probably have fried the battery management computer module and they cost several hundred £.

Edited December 28, 2011 by RichardW

[Nollywood]

The only way to get power to your battery, to open your trunk, is via the starter motor. This involves raising the car with a workshop jack, then supporting with an axle stand. You can then apply power via your booster pack - earth to the engine block, and positive to terminal 30 on the starter motor. This will allow you to pot the trunk, and start your engine with the booster pack via the battery.

You can investigate further once you've established you can get the engine running once more. I've got a feeling you've blown the fuse for instrument / dash. Good luck.