I have a 91 300TE wagon with 80k miles that just suddenly developed some lighting gremlins with interior lights. If you click the interior dome light to the setting where it should go out automatically once the door is closed it doesn't and the seatbelt portion just blinks non-stop. It also blinks continously while driving regardless if belts are being worn or not. The rear door courtesy curb lamps at the bottoms of the doors stay on continously whether the doors are opened or closed and I have had to remove the C red fuse in the fuse box to keep from draining the battery. I wondered if there was a lighting control relay that could be at fault or??? If anyone can help, I would appreciate the input. I love the car and would like to get this resolved.
No need to qualify a TE as a wagon. A TE *is* a wagon and can't be anything else.
I have an 88 TE and it sounds like something changed between 88 and 91. There's no link between the seatbelt warning lamp and the dome lamps on an 88. Either that or your 91 has developed 2 problems simultaneously.
I think the rear puddle lamp situation is an important clue and I suspect that the problem may be the rear door courtesy lamp switches. (The rear puddle lamps don't turn on when the front doors are opened.)
I'd open each rear door and remove the courtesy lamp switch that is located in the jamb between the upper and lower hinges. Very easy to do, nothing to mess up. You simply squeeze the retaining tabs (they're oriented up/down) and withdraw the switch from the jamb.
See if anything looks weird at the switch terminals. The lamps turn on when the switch *grounds* the lamp circuit so if a wire got disconnected from the switch and is touching the body the lamps will stay on.
The same switches are used to set off the alarm system so I'm a little surprised that you're not having trouble with that.
Check out those switches and let us know what you find.
I checked the switches at both rear doors, took them apart and reconnected to no avail. Puddle lights still stay on with all doors closed. I have not had any alarm issues. What controls the delay timer on the dome lights? Like I said, the seat belt warning flashes when the car is running and never goes off. This just started happening a few days ago and was not doing it previously which made me think a lighting control relay might be at fault. Everything else seems to work fine.
Ok, I sort of created part of my own problem...I put the fuse back in the fuse box and the seat belt and front dome light returned to normal operation. The lights in the rear doors, however, even after fiddling with the switches stay on when doors are closed. I took the lights out of each of them pending further info on what to check next. Wires seem normal and nothing is unusual looking...all other rear lights function normally when doors are opened and closed...what should I do next...?
I am having the exact problem, I was installing a new amplifier, and once everything was goin, i noticed that the interior lights were not turning off, I did what you have done and checked all the door sensors, and they seem fine, and i also came to the same conclusion that it could be the relay.
this is because after fitting everyting, i took disconected it hoping that it would sort the problem, so i really think its the relay.
Where could i find this relay so that i can take it out and search for a new part... hoping to sort it.
I hav also removed th C fuse, and i cant use my alarm....
hopefully we can sort this small but annoying problem.
Don't know if this is related but I had a weird lighting problem in my '87 300 TDT several years ago. In my case, the license plate lights wouldn't turn off, even when the key was removed (light switch obviously off). It was eventually traced to a short in the junction box above the rear headliner. This is where the rear hatch struts are too.
From the sound of things I'd wager ya'lls lamp control relay has started to give up.. Not all that uncommon. All the 124's/126's use the same relay, 126 542 0132. The relay is in the fuse box, it's long, about 5 inches and an inch+ wide.
I should have good used should ya'll be interested.
Need to replace the courtesy light switch in a w124 e220 cabriolet. Anybody knows how. I have been searching for month but nothing. I have removed the 2 lenses and have unscrewed the 2 screws......canno remobe the plastic holdre that holds the two switches
Help-interior lighting woes 91 300TE wagon 
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