Auto electric guru - please advise. - PeachParts Mercedes-Benz Forum

ah-kay · #1 01-30-2016, 12:54 PM

I am baffled by an electrical short in the 190D, W201 chassis. The car has a 'SOLID' short somewhere but I cannot see how.

Symptom - The passenger side front sidelight ( dual filament inside the indicator light ) and the rear tail/parking light is on with key removed. It is a solid ON, not a dim on. So it is a solid short. These 2 lights are tied together as per the schematic and is connected to fuse 14.

What I have done so far.

1) Remove all the fuses in the fuse box and problem still exists.
2) Remove the head lights 5 positions switch ( running lights, low beams, etc switch ) and problem still exists.
3) Remove the console and the problem still exists.
4) Measure fuse 14 for 12 volts and the side AFTER the fuse ( switched side ) has 12v with key removed. It shouldn't have. That is why the lights are on.

I am stumped as to what caused a solid shot and but 12V on the circuit. I suspect it is caused by a relay, may be the warning buzzer light relay. But I cannot find it.

Any help is appreciated.

vtmbz · #2 01-30-2016, 01:02 PM

It occurs to me that the headlight switch can be set to a park mode with only one side lit up front and back and that you could then remove the key, so I would consider the headlight switch circuit as the possible gremlin. Meaning it has power present with the key removed.

Steve_in_NV · #3 01-30-2016, 06:04 PM

Quote:

Originally Posted by vtmbz

It occurs to me that the headlight switch can be set to a park mode with only one side lit up front and back and that you could then remove the key, so I would consider the headlight switch circuit as the possible gremlin. Meaning it has power present with the key removed.

I think that feature lights up the drivers side parking lights. Unless your steering wheel is on the wrong side. I could be wrong.

vstech · #4 01-30-2016, 06:24 PM

This feature lights up either side depending on where the switch is set.

red55b · #5 01-30-2016, 08:11 PM

Check your grounds and any secondary grounds are secure

ah-kay · #6 01-30-2016, 09:00 PM

I don't think it is the ground. I do not think I switch the head light switch to the left. The headlight switch had been REMOVED. It is short by something, may be the buzzer relay. I need to locate it and check it out. Any idea where it is?

Jeremy5848 · #7 01-30-2016, 11:09 PM

Based on the OP's description, the short circuit has to be from a location that is powered with the key off/switch removed and all of the fuses out. There are only a few circuits that meet these criteria. I do not have schematics for the 201, only the 124. These two should be similar.

If the 201 has an alarm and if it's similar to the 124's alarm, I would check the circuits that run through the alarm module. My 124 diagrams show that the alarm gets power through two "auxiliary" fuses (located in the relay part of the fuse/relay box. If the 201 has something similar, and if the OP did not pull those auxiliary fuses when he pulled all the others, there's a chance that a short in the alarm is causing the running light to stay on. There is also wiring between the alarm module and the exterior lamp failure module; a short in the latter might also be a contributor although most of the circuits are fused. Again, I'm ignorant as to how much similarity there is between the 124 and the 201.

Jeremy

Alec300SD · #8 01-30-2016, 11:20 PM

Broken connection/ short in multiswitch on the stalk is probably the culprit.

You need to pull the steering wheel to be able to inspect it.

babymog · #9 01-31-2016, 03:14 PM

If not that, look for an aftermarket keyless entry, alarm, or remote start. Any non-factory wiring or installation is suspect. A local dealer chased electrical problems for a long time in a customer's BMW, eventually found a screw (aftermarket remote start) drilled through sheetmetal had pierced a wire harness on the other side.

ah-kay · #10 02-27-2016, 01:58 AM

Let me update this thread. The problem is resolved but not without a LOT of work. I ohmed out all wires in the side light circuit and do not find anything wrong. I decided to take out the fuse box. It is PITA because the location of the W201 fuse box is next to impossible to get to. Anyone who try to remove the fuse box cover would understand what I meant. The problem is a short inside the fuse box between the 12V and the side light circuit. Got a fuse box from a fellow member here and now all is well. This is an unusual failure mode but the car is 32 years old so anything can happen.

It is not the ground wire, not an after market radio, not the car alarm system, not the headlight switch. The fuse box is a solid mass and I cannot see how I could open it up without destroying it.

Jeremy5848 · #11 02-27-2016, 02:02 AM

Thanks for the update. Definitely not a garden-variety problem! Congrats on solving it.

moosejaw · #12 02-27-2016, 08:22 AM

That is a much better resolution than a "Hey I found the problem, my car caught fire from the short" kind of post. Worst/best case scenario you have kept your vehicle from being a total loss.