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