PeachParts Mercedes-Benz Forum - Interior Lights on W116:

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Interior Lights on W116:

My driver's side front interior lights don't work on my 1978 300SD. All other doors work. I installed new siwtches, but the driver's side circuit is dead. I assume there must be a control module for the lights, since the back doors turn on the back lights, etc.

Anyone know where it is??????

Quote:

Originally Posted by Doktor Bert (Post 2620090)

So the rear light comes on but not the front?

Try changing the bulb in the front it must be fused, very simple ;)

Right front turns on front lights, left and right rear turns on rear lights, but nothing from left front....

Quote:

Originally Posted by Doktor Bert (Post 2620101)

Right front turns on front lights, left and right rear turns on rear lights, but nothing from left front....

door button bad? try jumping the two wires going into the door button.

Quote:

Originally Posted by Doktor Bert (Post 2620101)

Right front turns on front lights, left and right rear turns on rear lights, but nothing from left front....

try taking the switch out and then touching the wires together and see if the light comes on......
before you buy new switches you should do this test to see if the problem is really with the switch.... try this test and post back

Does the key in ignition buzzer work?

-J

Quote:

Originally Posted by pixelsblack009 (Post 2620226)

LF is dead.....

Quote:

Originally Posted by compu_85 (Post 2620429)

Does the key in ignition buzzer work?

-J

Nope....

I'm a novice at this....but on my W116 78 300sd the front courtesy light wouldn't work as well. I was doing something else beneath the drivers side steering column and saw a eight or ten prong plug that wasn't plugged in. I placed it into the box on the firewall beneath the steering column area that said HELLA and my front light (over my mirror) my key in ignition and lights on buzzer now work.

Hope this helps.
Duke1
Mike

Sounds like the door switch for the driver's door might just be dead. Does your car have one or two? If your W116 is like my W126 the switch does not ground to the door frame, it has its own ground wire connected to it. Just something to check.

Does the fasten belt light ever come on in the cluster? If not its likely someone just unplugged the warning buzzer... understandable considering how shrill the early ones are. I don't have any W116 wiring diagrams, so that's one thing to check. On the W126 the ground "signal" from the driver's door switch is routed through the buzzer module, and if it is unplugged the interior lights wont come on when the door is opened.

-J

No power to the LF door lamp switch. All lights work execpt for the driver's door. No buzzer or seat belt lamp either. I will look for the relay!!!!! I'll bet it's unplugged!!!!!

Thanks!!!!!

If everything is working right you should see ground on one side of the door switch, and +12 on the other (when using a low impedance meter, like a digital one for example)

-J

Thanks!!!! Going to the snow in Yosemite today. Will check tomorrow....

For years, my dome light has been inoperative on only the driver's door. The passenger’s side front door light works fine and both rear doors turn on the rear seat area dome lamps, but nothing on the driver’s side front door. There is no power to the door jamb switch and I never could figure out why...until last night.

While changing the expansion valve, I found a square metal control unit, attached to the brake pedal bracket adjacent to the steering column. The unit was unplugged and marked with part number 001 545 52 32. This is known as the Safety Belt Alarm Relay, but it is much more than that.

The unit controls ONLY the driver's side dome lamp, but it also controls the key-on warning buzzer, the brake lining warning lamp, the seat belt warning lamp and the seat belt latch circuit.

When I plugged it in, my dome light worked!!!!! But, my brake lining warning and seat belt warning lamps were on continuously, along with the annoying warning buzzer anytime the key was inserted.

Inspection revealed part of the circuit board literally blown away from a short circuit. Since I did not have a spare, I decided to disable everything but the dome light circuit.

The attached photos show how to remove the brass contact lever on the warning buzzer's electromagnetic coil and which diode to unsolder to disable the brake lining warning lamp.

With these two modifications made, the unit will only function to control the driver's side dome lamp. This is a temporary repair until a replacement unit can be obtained.

Hope this helps....Robert

This mod is working nicely and no battery draw either.