I would personally guess that your switch (or relay) is the problem, not the resistor, if you are only getting low speed. Without looking at a wiring diagram, i think typically the resistor is bypassed in full speed.
Anyway, good luck!

Pic was taken with engine off, i.e. not charging. Right meter is volts, left meter amps. I have it wired with short jumpers in between the blower and blower connector for shortest path. I leave OE fan switch on high. If fan switch is on low, blower does not run with the controller. Not sure if that is bad for the controller or not when on low long term. Didn't do any harm in the short test on low. I'll probably leave the controller near its current location except mount it lower near the floor because it is cooler. If test goes well, I'll un-solder the pot, extend it with wires so it can be mounted somewhere I can reach.

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked