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Use the great tip contributed by Dana Franklin who discovered that Mercedes Benz sells just the solenoid valve alone for a lot less money. Buy the parts for the vacuum pump air valve switch for a 1985 500 SEL from your local Mercedes Benz (MB) dealer (part numbers were current as of October 1998. Costs were from Maplewood Imports in Minnesota, (651) 766-2333
www.maplewoodimports.com):
Qty 1 Solenoid Valve - Mercedes Benz #001-540-86-97 $24.00 each
Qty 1 Cable Connector - Mercedes Benz #008-545-11-28 $0.50 each
Qty 1 Cable Connector - Mercedes Benz #008-545-08-28 $0.70 each
Qty 2 Contact Bushing - Mercedes Benz #001-545-44-26 $0.70 each