OK, got a rear window that intermittently won't go up or down. First thing I thought of was the relay, but if you give the tailgate a good solid thump, it'll work again. This kinda leads me to believe it's wiring. My first guess as to where would be where the cable flexes when you close the tailgate, but does anyone know of any other common spots?

 

look where the wire connects to the motor and also check the roof switch on the driver side pull the rear interior panel off it the 3 or 4 bolt from the back also buy you jack is where the connection to the door is it about 8 wires into one big plug look at that i had so my trouble so just ask also if you disconnect the rear wire and jump a ground and a positive to the motor it will go up to put it down switch the wires opposite of each other. if you need it i can try and get some pictures for you

 

if you need to hit the tail gate then you should look at the gate closed switch it on the drivers side latch thingy on the tail gate