VIN# and relay part# please..

126 542 01 32 is the relay number for him. It supports 3 vehicles as far as I remeber.

Control Unit, Lighting/Lamp
MB# 126 542 01 32

Application List:
W124.050, 026, 028, 030, 032, 034, 036, 050, 051, 052, 061, 066, 090, 092, 128, 131, 133, 193, 230, 290
W126, 024, 025, 035, 039, 045, 125, 134, 135

Figured out the fuse blowing...Connections were grounding inside the housing. Just wrapped up the exposed metal and all good. The light is still on though so obviously the cooking did not fix it. Oh well...worth a shot. It has worked for me before with the other relay in there that controls the wipers.

Good to know about the 93 changeover. Here's what mine looks like:







and ready to be cooked:



Just gotta find a local junkyard out here in Phoenix.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Yep you had the same style as me. The silver race tracks had a burned area on mine that you could see but yours may not be as apparent. My lights also all worked. I would just get another if you can. Ill try and take mine apart and show you what a newer one looks like. Other than those heat sink/race track silver pieces look similar.

I apologize for resurrecting an old thread but it's relevant to my problem and may help others with similar issues.

The issue I'm having is on my '88 420SEL (US spec). The lamp failure light comes on when the headlight switch is turned full right (headlights and park). The right headlight is dim on low beam. The rear side marker lights do not work. Also the brake light circuit was bypassed by a PO. There is a feed wire run from the brake light switch back to the left hand rear light panel. The brake lights do work this way but I want to resolve the issue. I pulled the lamp monitor and a few of the solder joints at the pins appeared to have cracks. I repaired these and the lamp failure light doesn't come on now. All the lights still work escept for the rear side markers still. But this i think is an issue in the lamp panel. It did not solve the issue with my brake lights. I need to do a continuity check on the circuit. In it's present state it would prevent the cruise from working also would it not?

The other question I have is I see the lamp monitor module P/N 126 542 01 32 was used into the '90s. Does the part number remain the same on the newer part or would the module starting with 140xxxxxxx interchange with mine? Thank you for any help.

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1983 300SD
1988 420SEL

Dunno how good you are with the soldering iron?
You see the large contact posts. They are riveted to another electrical carrier e.g. metal strip connecting to the PCB. This method for making contact was used in the very early double sided PCB's and you guessed right, wasn't durable. I guess to charge the almighty rich Mercedes Owner (Stealership price $125/open range ~$65.00) for the relay/monitor, they continued this crappy way of connecting high current traces. After 20 years of service, dust, heat , cold, moisture, a little bit of corrosion builds up at the rivet site, adding additional resistance. Perhaps enough to throw all the sensitive circuitry out of wack. I had my in dash defective bulb, go on because someone decided to put a 10W bulb into the third brake light.

The way they check the bulbs, they simply split certain circuits into groups. The known is the total consumption of power (Wattage) all light bulb watts added together total power consumption. Now they monitor the current and voltage to a predefned value. If that value is not present it triggers the in dash. Down side, you'll never know which one!!!

Back to the rivets. If you are good with a soldering Iron, you can desolder the large contact posts, so that you can get to the rivets. Once the path is clear, put some solder to the rivet side of the contact and reflow it until it looks all covered without cold solder spots (nice and shiny). On the larger posts you'll probably have to heat a little longer (cold solder), but not too long, don't want to melt the plastic carrier.
Do this for all contact posts and if all goes well it will work again as supposed to.

Blowing the fuse, is probably related to a short after the oven excursion. Normally solder with a flux core has melting point, starting commonly at 650F or less, however there are plenty of different types on the market and each has a different melting point and characteristics. Chances are, something got soft and either came lose from a solder pad or shorted out. We tend to drop hot things.

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Mostly, I don't know notin, I just know where to look.
I am looking back, to over 30 years in Electronics Design.
Electrons don't care if they move in a car, computer or relay!

95 W124 E320 M104.992 - Because, I love to repair, naaaah!
Over 221,000 Miles
Cheers,
Norbert

Thank you oldtrucker for the advise and insight. I had an idea the monitor would read the rated current through a circuit to know is something was amiss. That's what has me stumped now with the rear side marker lights still out why the bulb failure light doesn't come on. It would only activate when all lights (headlight and running/park/) were on. I thought the dim headlight might the cause but apparently not. After reflowing those pins I found it doesn't come on.

Looking at the circuit diagram the stop/brake lights go through the lamp monitor. Whoever found the brake light circuit dead at the lights bypassed the wiring harness just for power and not ground. If there was an issue with the lamp monitor there wouldn't be power to the brake switch correct. Looking at the flow the circuit runs from the brake light switch through the lamp monitor and out to the lights. I need to locate the X21 junction which includes connection to cruise control and ABS.

The other question was the interchange between models for the lamp monitor itself.

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1983 300SD
1988 420SEL