[T77911S]

the first problem is the multimeter (MM). i dont think you really know how to use one, and most dont, so dont be insulted.

you dont measure voltage across a fuse, you should be measuring it with reference to ground. this it why i tell people to use a test light. also, a test light puts a load on the circuit as where a MM does not. also, the test light pretty much makes you use ground as a reference. you can also clip the testlight to 12v and probe for a ground or short.

you need to provide more details. where are you measuring voltage when you press the switch?
do you have a fues or a circuit breaker?
do the windows go up or down?
if the fuse blows, how do you have voltage on the switch?

first place i would look is the wiring at the door hinge.
i would aslo try unlugging the motor if you can.

if the fuse pops as soon as power is applied, that is why you can measure 12v across a fuse. a good fuse shows 0v.