Hi there,

The car is a 1999 model 4.2 quattro. You guys sounds as though you know whats going on, and please forgive my ignorance, but could you tell me where to located the connections which are suspected badly grounded. I'm still new to the car (and apart from relacing a bad aerial mast) haven't done anything else on it), I bought it only 4 months ago.

Thanks again for all your help.

chris

 

... if that is the problem.

Tom

 

Hi Chris,

We have discussed two kinds of ground connections: (1) wires attached to each other within a wiring harness, which lead to (2) electrical terminals bolted to the chassis.

I don't know where the in-harness connections are -- the service manual specifies only which harness, for example B108 is "in wiring harness interior, right, rear".

The chassis attachment points are better known. The "JPG of the TSB" posted by Paul shows how to get to ground point 43.

On a 2001 car at least, ground points 59 and 60 are just in front of the left and right low level brake lights, respectively. You can access them by removing the covers in the trunk as if you were going to change a brake light bulb. Start with the battery compartment cover and its counterpart on the left side, then remove the little access door ahead of each brake light. Each ground terminal (on a 2001 car at least) has a brown wire and is bolted to the chassis ahead of and below the brake light.

If you can catch the car with the high level brake light stuck on, the simplest way to determine which of the three grounds (if any) is at fault could be to leave the headlights on, then (1) move the ground connection wire near one then the other low level brake light while watching the high level brake light, and if that doesn't turn it off, (2) remove one then the other low level brake light bulb. If removing either bulb makes the high level light go out completely, that bulb, socket, or it ground path is at fault. If removing either bulb only dims the high level brake light further, then the B104/43 ground path is probably at fault.

Tom

 

I checked the cars rear lights over the christmas holidays, and suspected a faulty connection between the brake bulb and the holder.

Whilst removing the bulb i dropped it onto the floot of the boot.... the filiment broke so I replaced it. I don't have the problem anymore so suspect (as mentioned in the subject) that the bulb was at fault.

many thanks for all your help.

chris

 

You probably fixed it permanently, but if not, a bad wiring connection to a bulb socket is likely to blame. You can gain confidence that the bulb was at fault by turning on the headlights and watching the high brake light while manipulating the wires to the bulb you changed.

Tom

 

Any ideal where my ground wires are?

When I apply the brake my lights come on.

When I let off they do not stay on...
I have changed bulbs but nothing at all.

 

I have this problem... The year of mine is 2006 A6 .. I would greatly appreciate it I can get some help.

 

You are posting in the wrong forum but maybe the brake light switch? They get worn and need to be adjusted or replaced on our 1994-2002 Audi A8 and S8 cars.
Careful if it is this switch do not drive the car. The transmission torque converter clutches can get burned out if this switch is not working properly, the transmission declutches a lot thinking you are hitting the brakes.

 

If a double filament bulb has one filament broken, it can lay across the other filament and create a sneak circuit.

Weird things like hit the brakes and it back feeds the running lights and cluster lights because that one double filament bulb serves those two circuits.

Check for: 1) broken filament in double filament bulb creating a cross circuit 2) melted contact **** on the bottom of the bulb also creating a crossed or backfed circuit and 3) check that you didn't put a single filament bulb on a double filament socket...the single contact on the bulb bridges the two contacts in the socket.

My money is on a broken filament, especially if the issue is intermittent.