I am trying to finish up the last few jobs on my 1993 300TE and I discovered the other day that I have no power to the right rear taillight bulb socket.
The turn signal and brake lights in that same lamp housing work fine and the taillight on the left side of the car works fine.
This evening I pulled the fuse out of the fuse box that was labeled as going to the right rear taillight and carefully cleaned both ends of the fuse and then checked to see if I was getting power through to the ends of the fuse.
I was getting power through the fuse but I still do not have any power at the right rear lamp housing.
I have also removed the cover from where the plug on the end of the pigtail plugs into the socket on the wiring harness and I do not have any power going to the pin on the socket that should transmit power to the bulb position for the taillight.

Anyone have any suggestions as to where else I could look to see where the problem might lie?

The power goes thru whats called a bulb failure control unit, is in the cover at the left front fuse box take out the 6 screws and you will see it its marked "hella", ill try to l look up a wiring diagram, cant at the moment

check out this thread:

http://www.peachparts.com/shopforum/tech-help/406075-w124-e320-lights-not-working.html

It ended up being a bad solder in the N7 relay (Bulb failure monitor)

I removed the exterior lamp failure module and took it to a friend who is an electronics expert. He found two places on the circuit boards that looked suspect. He re-flowed those two spots and I reinstalled the module back into the car. That fixed the problem and I now have working taillights on both sides of the car.