If you google the problem you get a few mercedes source videos where they're trying to get you to buy a 13 dollar video on how to fix this problem.

One of the snippets is to get to the plugs and try to power the motors directly. You say the plugs are hard to reach in your first post but you might want to try and do this at the switch?

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!