You bet. Look at the big coils in the heater resistor. Your rheostat will have to have coils like that. In theory, you can use a switched power scheme using pulse width modulation of a MOSFET switch with a low on resistance. But seriously, just rig some switches to the existing fan resistor. Forget about the rheostat.

Edit - oops sorry. Just checked your link for your Rheostat. What you have there is a micro controller based pulse width modulation system with a MOSFET stuck to a heat sink. This will work if you get one that can handle the current going to the motor. I recall its around 10A.

Sorry I didn’t check your link. I do think something like this will work.

Update - aww man. Put in a new pushbutton unit on the 300d. It is better. It doesn’t just blast hot air for no reason. Fan still doesn’t turn on on EC unless I push on AC or defrost buttons first.

Good luck with your fan. I need to trace the fan circuit on EC. On my 300sd the blower always turns on when the fan button is on and the system is on AC. Maybe I’ll jerry rig mine with a switch to the fan resistor.

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79 300TD “Old Smokey” AKA “The Mistake” (SOLD)
82 240D stick shift 335k miles (SOLD)
82 300SD 300k miles
85 300D Turbodiesel 170k miles