jtaitch191

So I have a 93 s4 and my left tail lights are out and I'm kind of scratching my head... bulb and fuse are good. Brake and blinker lights work on the same side and bulbs, can someone help ?
Thanks- Joel

UrS4boy

This post was originally intended to show that the trailer connections are in PARALLEL with the normal DOT rear lamp holder bulb filaments. However, you can use the info and a multimeter to track down your problem.

First of all, some basics:

a) The lamp holder is held into the taillight via a 90 deg turn "arrow head".

b) each left and right lamp holder is connected to the C4 lighting wiring harness via a four pin connector.

c) the DOT lamp holders have two, 2 filament 12V bulbs (typically a P21/5W, (5W for the running light filament and 21W for the brake light and turn signal filaments))

d) the connections to the four bulb filaments are done by stamped metal plates that mimic printed circuit boards

e) a some points there are metal traces that seem to disappear into the lamp holder, but then show up again as a contact for one of the two lamp filament contacts on the base of the bulbs

f) the ground for the bulbs is on the outside of the base of the bulbs. Pin-wise this is "31" which runs to both of the two lamp holders.

All that said, here is an annotated photo of a right rear lamp holder showing the metal traces and how any trailer light spade connections would be in parallel with the vehicle lamps.

HTH