I've had trouble with mine in the past where it makes a buzzing sound from the relay. All I did to correct it was to unplug the control wires, clean the contacts and re-install. It's been fine ever since (knock on wood...).

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250