Variable fan speed for the camper

The T3 VW camper vans came with a three step fan speed switch. Maybe it broke just like that, or maybe it was due to the kids playing with it endlessly. No matter what, the broken switch was a good opportunity for an upgrade. I ordered a 15A PWM motor speed controller which I thought should be big enough. Its potentiometer was broken on arrival, so I got a more rugged one from the local shop.

Connecting it was more complicated than I thought. With the original three step switch, the motor was directly connected to ground, and the highest tier connected it directly to 12V. The other two tiers had resistors in series. My naive expectation was that the ground would be common between source and motor, in the PWM unit as well. But instead the plus was common and the minus was PWM switched. So I had to search the connection from the motor to ground and cut it.
In the end, it works like a charm…

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