That sounds ALOT like what I went thru with my SD. If you can manage to hard wire the motor directly to a KNOWN ON power source (12VDC of course) If it works, there's a fault somewhere else. The next likely problem is with the resistor pack.. beyond that is still a mystery to me. In the end it was the motor that had failed. Couldn't get one so I grafted one from a Nissan onto the flange plate and it worked remarkably well.

But to answer your question, yes, with a switch inline and a MINUMUM 25 A fuse.

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2002 E430 4matic (212,000km)
2002 ML500 'sport'

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