Rear tail light is out on my 88 300ce
 

I've tried to narrow down the problem by swapping the bulb, swapping the assembly & swapping the big black light relay in the relay box. Apparently no current is reaching the plug for this bulb. After reading the wiring diagram in the Haynes manual, the only other thing that I can think of is the headlight switch. Does anyone have any suggestions. The offending light is on the left (driver's side). Thanks in advance, as always.

In this order:

Check the connector on the taillight for spread socket for the pin on the that circuit. Also make sure the holder isn't spread -- I loose the side maker lights from this problem once in a while, they are quite easily bent.

Check for voltage at the correct wire on the headlight switch.

If none, switch is bad, replace.

If there, check continuity of wire (broken someplace), in which case I'd personally run a new wire and cut both ends of the old one after makine SURE it doen't juntion somewhere, and that the wiring in the trunk hasn't been pulled or cut by something.

Peter

I'm not sure I understand your first paragraph. I swapped the assembly to the right side & plugged it in & the tail light bulb lit up perfectly. I swapped the right assembly to the left & the tail light bulb didn't lite up. Do you mean that in the connector itself the pin bends out of shape? How do you fix that? I think I already measured voltage in the subject pin & got none, but I'll check again tmrw nite. Thanks.

MB uses a sleeve in the female part of the connector. They can split, and fail to make good contact.

You should have voltage at the connector -- if not, either the switch is bad, or the wire between the right and left taillights is broken.

Peter