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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3663
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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I have a 2000 Mercedes S430 with only 70k miles on it that

Customer Question

I have a 2000 Mercedes S430 with only 70k miles on it that runs perfectly. The only problem I'm having with it is that when I start the car, the headlights/taillights stay turned on (even though the manual headlight switch is in the "off" position. Upon turning the car off, the headlights/taillights turn off. What could possibly be the cause of that?
JA: Have you checked the bulbs? Have you checked the connection?
Customer: Yes, all the bulbs are fine and working properly and all of the connections are in good shape with no corrosion or rust issues.
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I have a used car lot and a mechanic on hand. We checked all of the bulbs and I even switched out the headlight switch with another one but the car is doing the same thing.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Mercedes Mechanic about your situation and then connect you two.
Submitted: 3 months ago.
Category: Mercedes
Expert:  Lou P. master tech replied 3 months ago.

Hello, that usually is the cause of a failed headlight switch. if the switch is disconnected or fails the modules will turn on the lights as a safety backup. you will need to have the switch inspected and replaced also check the power supply to the switch. let me know what kind of info you need and i can assist, i see you already switched out the headlight switch so next step is to check the power supply and also make sure there is no water found in the front left and right fuse boxes in the engine bay.

Expert:  Lou P. master tech replied 3 months ago.

PINS 5 AND 6 of the headlight switch should have battery power, they are grey with a red stripe. they connect from the headlight switch directly to the left front sam which is the control module that attaches to the bottom of the fuse box.

Customer: replied 3 months ago.
I already swapped the headlight switch and the car is doing the same thing. As far as the power supply, everything checked out. I do not see any signs of water damage in any of the fuse boxes. I had been reading that the left front SAM (signal acquisition module) controls the exterior lights (headlights / taillights). Is that true? If so, if I get a used one from a salvage yard from the same year and model, does it have to be programmed all over again or is it a plug-and-play install?
Expert:  Lou P. master tech replied 3 months ago.

if you get one from a model with the same options then yes should be plug and play, they are not vin coded in this model.