Big, Fat Electronics question for all y'all.

[tw]

Originally Posted by footfootfoot

I'm to check the resistance of the fan?

Fan is a non-linear load. Measuring resistance will not say anything useful.

A brushless fan contains transistors that power cycle (fully off or on) to spin.

Start with the circuit wired. And resistor set to some desired fan speed. Then measure voltage across fan and voltage across 25 ohm adjustable pot. And finally, measure current through pot and motor. Or remove the pot to measure its resistance.

Those numbers will confirm parts are working per the hypothesis.

BTW, also take an ohm measurement of any 120 volt incandescent bulb. That number will be used to demonstrate another non-linear load.