You have a ground problem or loose wire. You will have to check from top to bottom. Do you have a ETM? (electrical troubleshooting manual?)
They are in the CD we offer in Partsshop.
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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM