[200q20v] Headlight and tail light woes

[david_haupt at agilent.com]

I had been dreading the job.  The DPO told me he'd installed an aftermarket
harness for the headlights.  First one, then the other, went dim.  Not out,
but dim.  Obviously not bad headlamps, but a wiring problem; something went
high resistance.  The idea of troubleshooting a non-stock harness instilled
great fear in me!  However, it was not to be so bad.  I quickly identified
the problem right at the bulbs.  The 'common' wire was badly corroded.  Some
400 grit paper on the sockets and bulbs, and I had headlights again.

The car has 80/100W H9004's in it.  I have never used "flash to pass" the
entire 2.5 years I've owned the car.  Therefore, the common wire has never
carried more current than either of the individual filament wires (since I
acquired it).  Why would the common pin get so grungy, while the others look
good?  The pins and socket were bone dry, no grease.  Would the listers
generally approve of applying dielectric grease, to reduce the possibility
of water ingress?

I also found a prize - the original wiring harness on the drivers' side is
still there, still live with electricity.  The common pin on that socket is
just as corroded as the one on the new harness.  That's three for three.  I
think I have two sets of live wiring in parallel here.

As long as I was fiddling with headlights, I installed the new rear tail
light I recently acquired from Paul Luevano.  Nice fit, just popped right
in, and there was enough sealing 'goo' from old and new to cover the
opening.  Then my wife and I checked all the rear lights.  The brightness
from side to side is not uniform, so I dug into it.  There were dual
filament bulbs in single filament sockets and vice-versa.  A closer look
revealed that the sockets for the backup lights aren't the same.  One of
them uses a bulb with pins set back from the base equally, while the other
one uses a bulb with unequal setbacks.  That's consistent with a dual
filament bulb, but there's only a single contact in the bottom.  Anybody
have the actual Audi PNs for the correct backup sockets?  I can look up the
correct bulb numbers in ye olde owner's manual, of course.

Between the DPO, the price of parts, the number of "little" things that take
six hours to repair, this car has been undrivable half the time I've owned
it.  There's good news in that - I haven't added many miles to the odometer!

Dave