Two things, the connection between the new unit and the wire harness has to be a 100% good solder connection to carry the load. The other thing is the ground. There should be a ground connection near the headlight where a wire bolts to the inner part of the sheet metal. Make sure that is clean and tight.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
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