87 5kCSTQ Mysterious Brake Light

[nicksimc]

>From: Paul Meyers <paul.meyers at citrix.com>
>To: "'quattro at audifans.com'" <quattro at audifans.com>
>Subject: 87 5kCSTQ Mysterious Brake Light
>Date: Tue, 24 Jul 2001 11:28:36 -0400

>So, during the year storage in the back yard, I bashed a quarter-sized hole
>in the right rear taillight assembly on the Gray 87. Chris Semple sends me a
>new taillight (thanks, Chris). I install it last night. Easy to do with deep
>8mm socket. Hardest job is reworking the sticky black goo used to keep water
>out. I go for a test drive and on comes the warning light telling me my
>brake lamp is kaput. I go around to the rear of the car, having son press
>brake pedal. Sure enough, the brake light no longer lights. I know it
>worked, since the car just passed the state safety inspection. So I figure
>the light bulb must have coincidentally burnt out. No, filament still good.
>I check all the fuses, Nope.
>
>Then I turn on the headlights. Now the mysterious behavior. The brake light
>now comes on with the taillight! Other brake lights work normally, but this
>one now only comes on with taillight and fails to work as a brake light.
>
>No connectors were removed or reattached in the lens replacement process.
>The bulb carrier just snaps out then snaps back into the new lens assembly.
>There is no electrical contact between the bulb carrier and the lens
>assembly, so it can't be a ground problem.
>
>What gives?
>
>Paul Meyers
>Gray 87 5KCSTQ 1.8bar eurolights fuchs 147 kM
>Pearl 88 5KCSTQ 1.8bar eurolights fuchs bilsteins 128 kM 2pc-em k24 turbo
>Repainted Pearl 87 5KTQA 1.8bar eurolights TT wheels bilsteins 203 kM daily
>driver
>Blue 86 5KCSTQ parts car

I recently had the brakelights go out on my '82 4ks, and I found that the 
bulb-carrier was indeed the problem .  When I was attempting to get it 
working, I 
experienced  problems similar to yours.  It turns out that one of the tabs 
going into the multi-connector had heated up and melted the plastic retaining 
'blob' that 
secured part of the metal circuitry on the carrier, and this caused a ground 
fault.

I would still check the trunk lid harness as that seems to be  where most 
people have a problem.  It wasn't an issue on mine since it had the old-style 
trunk which 
has no wiring connected to it, but as yours is a later model it might have 
that Achilles' heel.

Good luck,

Matt
'82 4ks
'84 4k