How do I find the engine cooling fan switch in a 1990 lumina van?

SOURCE: is there an inside switch for the rear door lock on the 95 chevy lumina van

if you mean for power locks the same power lock activates all the locks

SOURCE: what is fuel pressure out put for 1989 chevy lumina w/v6 engine

TBI-26 to 32 psi
PORT INJ.40 to 47

SOURCE: Bad heater fan motor in 1990 Chevy Lumina APV van.

It on the fire wall. Look up under dash from under the hood. You'll need a 9/32 nut driver to loosen the screws.

SOURCE: where is the cooling fan switch located on my 1994

should be on the side of raditor passager side

SOURCE: When my 92 chev van Lumina gets warm it stalls and won't start till It cools down. What could the problem be.

You'll need to get more information. Find an auto parts store that offers free engine code readouts and have them tell you what the engine computer has detected. This will shorten the long list of possible causes. Post again with the results - you may get to post your own solution.
I've had a bad fuel injector driver transistor in the computer (throttle body injection) and an ignition module do this to me.