w124 tail light problem
 

I have a 1993 300E and have an issue with the passenger side tail light. All other lights in the cluster work, I.e. turn signal, brake light, etc. I used a wire tester and there is no power to the lamp. Can someone help me out with where the rear tail light wires come from? I would like to check the power at the source.

Also, does anyone know where to purchase a rheostat? My interior dash and center console lights stopped working as well. Thanks!

Check fuses 1+3 (8 Amp)
 

Power for left (Driver's)tail lamp from terminal #9 on the External Lamp Failure
Monitoring Unit [N7].

A lot of people generally forgo the rheostat if it breaks, and jumper the dial so lights are on 'max bright' considering dash lights are quite dim in this car. Or just do this anyway to get more light. But if they're just out, maybe another fuse to check first.

Replace fuse #3 in the under hood fuse block. They can look good but really be bad. That fuse supplies the power for the all the things you mentioned.
Good luck,
Paul

Also check the metal strips in the taillight housing...over time they loosen with vibration and lose their seating...enough to mess up the connections to the bulbs...

Thanks for all the helpful replies. I used a current tester on the #3 post and there is no power to this post, nor the #4 post for the fog lights. Before I go tearing apart the fuse box trying to figure out what is wrong down there does anyone have any helpful advise? I have attached a photo of my fuse box and what appear to be relays at the top? (not for sure if that's what they are) Thanks again... :)

Assuming the relay is bad does anyone know a good place online to purchase a new one?

I had a similar problem with my 1993 400E. All the lights except one was getting power. I took apart the tail light assembly (pulled the metal out of the plastic) and used some fine sandpaper on the contacts thinking it was corrosion that was causing the problem. When I put it back together it worked. As someone mentioned in a prior post, the metal strips in the housing could lose their contact and maybe that was the problem in my case too. In any case, it was an easy fix, versus tearing into the fuse box.

I will give that a shot, however I already tested the fuse and I know it isn't getting any power so I assume this is why the dash lights don't work either.

Do your fog lights also not work (no power to fuse #4)? If you're sure about your testing method, no power to fuse #3 appears to be the problem. While you're trouble shooting, take a look at your fuse assignments. It doesn't look right to me, particularly fuses 7 and 10, and maybe fuse 11. They may be the wrong amperages, none of which should cause the lighting problem, but there are some pretty expensive components on some of those circuits.

Did you check for power on fuses 3@4 WITH the headlight switch ON ?. If you did, then the headlight switch is the next place to look. Remember the rear lights can be turned on individually by turning the headlight switch to the left. Also remember the fog lights will only work with the headlights on LOW beam. Keep us informed.
Paul

Take the light apart yet?
 

I had a similar problem on my 93 300e, passenger tail light kept going out. I ended up completely disassembling the light fixture and found that the metal piece inside that the bulbs seat in was off of a pin at one point, allowing it to flex and not make contact with everything it was supposed to. If I remember right it's a keyhole type attachement, and you're able to slide it to one side to remove it. I also found the snap cover on the wiring connector was loose, allowing the contacts to float around a little bit.