W126 420 SEL Dome light diagnosis help...
 

Ok, spent a few mins toying with the SEL again...

Here is my problem. When you open the drivers door, no dome light comes on.

When you open passenger door, or either rear door it works fine.

I immediately suspected the door contact switch, so I swapped passenger and driver side in the front (assuming that if it was the switch, the problem should alternate sides) , and the light system did exactly the same thing.

Passenger side lights up, drivers side doesnt.

I know that the drivers side door contact switch goes through the seat belt warning / headlight warning "buzzer" but that works fine.

Next thing im thinking is there is a bad ground to the contact switch.

One side should show ground constantly, and the other side should not, unless the circuit is completed. Is this correct?

Also, there are two sides to the contact switch, one that has a shielded terminal (in some sort of plastic sleeve) and one that has an exposed terminal.

Anyone know off hand which one is supposed to be constant ground?

Any other ideas of what might be causing this?

Thanks again.

George - new e-mail george@parts4sale.com

1996 C220 - 109k miles
1989 420 SEL - 243k miles

Try a warning buzzer relay, it has 2 functions & one is to turn the dome lamp on from the LF door. You could remove the warning buzzer relay & remove the OUTER black plastic cover & see damage on the printed circuit if it's bad.

Could the one function be bad independent of the other?
 

I.e. could the warning buzzer still work, but the dome light not?

Thanks again - George

Yes it happened all the time when the relay printed circuit burned
buzzer still work,but the dome light not.

Ok I guess that is the problem
 

What is the best way to get to it? - How much does it cost? I've only had the 126 for a few days now and dont really know my way around the car yet.

Thanks again,

George

The relay is locate under driver side lower panel just follow sound of the buzzer should not hard to find it part number 004-545-07-32 you can find it at FastLane.

The buzzer should be attached to the side of the cruise amp on your car. The cruise amp is bolted to the brake pedal pedestal, silver box about 6x4. The buzzer will be mounted on the inboard side. You will have to pull the driver's side lower panel to access.

Does anyone know if it's located in the same place on a W124?

buzzer
 

I have a '90 300E and hated the "buzzer from hell", so I took out the box which contains the buzzer and threw it away. I then found out the hard way that the dome light when the driver's door is opened did not work because if that, so i cut three of the wires going to the box (i can't remember which colors they are) and spliced them together. Now everything works and I never have to hear that horrible screeching again. -- Mike

I was thinking of another solution
 

Basically - If you were to run two new wires from the driver contact switch, to the passenger side contact switch,

As follows:



--{ } =========================={ }----

where the two door contact switches are in parallel

Wouldnt the car just assume that the passenger door was open any time either door was open.

All these contact switches do in fact is basically connect the two wires at the switch, one of which is supposed to be a constant ground?

My buzzer works per se, but If I can get the dome light working without replacing it, I really dont have an interest in replacing it.


If you remember any more info on what you did, Please let me know,

Thanks again,

George

Mikey - Where is the box located on a W124?

I don't know for sure on the 124's. I would expect it to be in the same place though, since 123's are in the same general area.

The "buzzer box" in a W124 is located just to the right of the steering column attached underneith a weird "finned" box that has some connections plugged into it. The buzzer box is black and is rectangular and is not big (about the size of two relay boxes put together). -- Mikey

So to access it, I'll have to pull out the gauge cluster? Is it accessible from under the dash?

Yep...you have to remove the cluster. If you do not know how to do it, search for how to remove it on the board...otherwise, let me know and i will tell you how. -- Mike