Power Windows - Master Switch - Fault or not?

Hello there

I have a Camry 1992 3.0ltr V6 saloon.

The rear left power window has stopped working. I have replaced the motor and regulator.

The window will go up, but not down. To check it wasn't a faulty motor or regulator I tried a different one and the same thing, moves up but not down.

I tried a different switch, still the same.

I then got my test meter out and found the following.

From the rear door power window switch I am getting a voltage at the motor for both up and down actions.

From the master switch on the drivers door I am only getting a voltage on the down action.

After thinking about this for a while I can only presume that the master switch allows for the voltage polarity to be reversed dependant upon whether the switch is being pressed up or down.

So, If I am correct, the master switch is not allowing a ground connection for the down movement.

With the master switch taken out of circuit I do not get any voltage at the rear door switch.

I then thought that I could prove this by finding the voltage for the down connection, and take a flying lead from the other motor connection to ground. This blew the main 30amp fuse, however, I didn't disconnect the cable from the motor terminal, so this might have caused a dead short with the presumed faulty master switch.

Could someone tell me if I am on the right track with this one, and if not, what might be the problem other than a faulty master switch.

Many thanks