A common trait among older Audis (funny to watch, a pain to suffer) is the "Christmas Tree" tail light syndrome. The symptoms are random seeming functions of the various lights in the rear clusters. You signal left, and both brake lights flash as well as the left signal. At a much diminished brightness. You turn on the lights and the whole darn cluster glows dimly. This is caused by the "minimalist" approach Audi seems to have taken with some of their wiring specifications. The entire tail light system, both sides, is grounded through one small brown wire. Eventually this wire ages, perhaps corrodes a bit, it's connections become poorer, and it just won't handle the current required any more. Due to another interesting feature of much Audi wiring, that devices when "off" frequently have their hot side grounded, the voltage present at the desired lamp takes another path of lesser resistance: through the other lamp(s) "backwards" to their grounded hot side. This may seem odd, if you think of the tail light assembly as being "grounded", but it isn't any more. It has a crummy old wire presenting 10 or 20 or 50 ohms to ground. So the active lamp and the brown wire (it's more of a resistor now) act as a voltage divider and the whole ground portion of the tail light cluster(s) sits at some voltage between 0 and 12. The solution is to add a pair of adequate grounds to the clusters. These assemblies are like giant scale PC boards. There are metal traces running all over a big piece of plastic, leading from the terminal strip to the various lamps. You first remove the wiring harness from them, usually by squeezing a couple of snap locks on each side. (At least these don't seem to break, but I wouldn't do it below 50 degrees F anyway) Then you remove the "circuit board", again usually by squeezing a couple of big tabs to release it into the trunk area. Identify the ground track. On my 5k I had to drill a hole through the ground track and attach a ring terminal to a bolt through this hole. On the coupe there is a convenient 1/4" male tab on each one - as if they knew this needed to be done! You lead a short 14 or 16 GA wire from here to a nearby location on the trunk metal. Try to pick somewhere that stays dry and will keep your new wire safe from physical abuse. Use an existing bolt to hold a ring terminal if you can, if you must, drill a small hole and use a small sheet metal screw to hold it. Work neatly, solder the wire to your terminals, and use heat shrink tubing to keep them clean. Use dielectric gel on the contact points.  |
