Be sure that the sensor under the rear seat has been disconnected. It is rare to still see them. They are round cylinders that were used to detect vehicle movement. The problem is that it is filled with Mercury, the Merc is temperature sensitive and there is a problem.

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Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM