Cabin fan has only one speed - MAX

[Yendor]

I have the identical symptom on my 89 GQ. 0-3 nothing, 4 = flat out (and have to yell to talk with passengers over the fan noise). Will check it out when I get home tonight. Is anyone aware if the componentry is in roughly the same places?

Yes the resistor is in the same position on the GQ.

If you can't see it just follow the wire harness from the interior fan motor this will lead you to it.

As per my post above (especially with your noisy interior fan) you will need to remove and inspect the fan motor before replacing the resistor.