Why On your 1984 gmc 3500 pickup all the power windows work except the passenger side front it must be the switch or motor how do you diagnose which one?

Answer 1

remove the switch from door panel. Put a test light on each of the two wires. Then push the button up and down. If light comes on, that side of switch is good. Test other wire same way. One wire is for up and the other is down. If you get positive test on the switch, problem is probably the window motor. To test this, you will have to remove door panel. Unplug motor and insert test light into the removed plug. Again check both sides with the switch button. You can do a more definitive test of motor by running two wires (hot and ground) to battery and then touching other ends to prongs of window motor. If good, the motor will turn. Reverse the wires for opposite direction.

Tests must be performed with switch on.

If you get positive results on all tests, you probably have a ground problem.