Ok, just checked it. Both transistors are showing 1.5Kohm on 3-4. I checked the voltage and got about 2.6 volts between #1 and ground with the ignition on, and the blower speed on any setting. When the blower was off, intermediate setting, or high, all the voltages were around 2.6 volts.


Is it possible the MOSFET is bad in both transistors? When I check the resistance on some of the other terminals with the transistor disconnected, I get weird resistance values. For example:
across 1-2 ~10.85Kohm
2-4 same value 10.95Koohm
1-3 1.5Kohm
3-4 1.5Kohm
1-4 is open (really high)
2-3 is 12.5Kohm


I find it hard to believe that both 3-4 AND 1-3 should be 1.5Kohm and (1-2 and 2-4 = 10.9Kohm) are the same.


What do you think?

 

If power transistor is conducting and bias on line 1 is low/zero volts, then transistor is bad. Bias voltage is applied via line 1 to modulate voltage passed to blower. 12V causes full voltage to blower, something much lower causes power transistor to open (blower off).

You will need to backprobe line 1 to measure voltage while commanding different blower settings.

good luck