ARGHHH. '94 E320 Dome light issue HELP
 

Dome light no longer works when ANY door is open. I've tried all the positions with the light switch. Am told the relay could be bad in the dome light assembly. Any ideas there? Does that relay effect any temp controls as well? And yes, I've checked the fuses.

Hate to ask the obvious, but did you try replacing the bulb? I can't remember exactly, but that overhead assembly clips into place and can be removed by pulling down on the edges. I remember it being fairly snug..... Also, I don't think there is a relay involved with the function of the dome light.

J. M. van Swaay

If you've checked the fuses, and the bulbs, then my next question is whether your vacuum pump is functioning properly...i.e the connection. The latter was based on my recent experience with dome lights (won't come on when doors opened) and climate control vents that would not open. As soon as replaced the pump, my problem was solved.

Bulb is good as I can turn the light on by sliding the switch to the "on" position. There are definitely two relays involved with the dome light. One in the dome light itself and one in the dash.

In the dome light, is a sensor for the climate control with a vacuum line running to it. This is not what you mean is it? Which vacuum pump and where was it?

Curiosity got the better of me--took a look at the wiring schematic.

Dome light assembly is E15/4, contains 5 elements, dome light, reading light, and 3 seat belt warn bulbs. Also contains the switch and an electronic control circuit. (control circuit is denoted by a transistor symbol...) No relay is shown. Power feed for all light elements is fuse number 9, power feed for control circuit is fuse number 5. Ground is supplied from connection point W4. If there are relays involved in the function of the dome or reading lamp they are not shown on the schematic......

Send me a pm with your email address, I'll send you a PDF of the schematic.

J. M. van Swaay

IIRC the dome light and seat-belt warning light are controlled by a relay/control box behind the instrument cluster, usually fails on though.

Yes, I think I see the module you are referring to. N2/4 is located behind the cluster and is identified as "seat belt warning module". From the schematic, there is a single input from the seat belt warning module to the control module located in the overhead lamp assembly. It seems logical that N2/4 would only affect the seat belt warning lights.......

Does the "seat belt warning module" also have an effect on the dome light??????

Maybe there's more to this than I thought!

J. M. van Swaay

I believe that it is responsible for the delay. Several times I've read of 124 dome lights staying on and the belt-warning light continuing to flash, and the warning module is resposible. It would follow that this could also be responsible for the lights not functioning, I'm making the assumption that the seat-belt warning light is not flashing also (OP?).

Vacuum & Interior lights
 

Obviously, the vac operates the vents, but was this a coincidence or is the door lock vac system really connected to the interior lighting system? Is this interconnect common to most MBs or only specific models / years? If these systems are connected, how so? Or am I missing something?

There is no connection, vacuum or electrical, between the vents, dome lights, and lock-pump in the '94 E 320.

I'm still kinda "stuck" here. If I can turn on and off the lights with the switch, the buzzer does come on...do I head for the relay behind the dash first or the dome light assembly?

Bulb is good as I can turn the light on by sliding the switch to the "on" position

Is it the dome light bulb that comes on, or is it the reading light bulb that comes on. (or do they both come on?)

Again, forgive me if I'm asking the obvious here, but there are two bulbs and your post refers to a single bulb...................

J. M. van Swaay

And when this is resolved, can we also look into what is causing my 87 300E dome light (the lamp that comes on when the doors are opened) to flash on and off when door is open or in delayed off mode? Already swapped another complete unit, does the same thing. Am I looking to replace the seatbelt relay? Thanks.