1996 Aerostar XLT driver/passenger window works only intermently?
Replaced the switches in the doors to no avail....

 

Likely the wiring harness going from door to inside of van has begun breaking the stranded wire. Someone correct me if this wrong, but I believe the power feed to the driver's side door also feeds back to the passenger side, since the DS switch works both windows.

My windows were going up s..l..ow..ly until I replaced that wire. It breaks from the repeated wire flex from opening/closing of the door over the years.

Take of a piece of clothes hanger wire and fashion a small, closed loop at one end. Open the door fully. Remove the door panel. From inside the van, push the hanger wire, loop end first through the wiring until you can find the end inside the door panel. Attach a new wire of similar or heavier gauge and pull it back through the wire loom, splice each end and that should solve your problem. If your fish wire repeatedly hangs up, spray some silicone lubricant into the wiring loom or else use a smaller loop.

 

while the door trim panel is off, spray lubricating oil in the mechanisms at the bottom; spray silicone into the felt tracks.

you can find out which is the bad wire by checking the wires on the back of the switch, get a new long wire, splice it to the bad wire at the switch, run it through the door rubber "accordion" as suggested by aerocolorado using a straightened wire hanger to get it inside the kick panel, and then follow the wiring harness inside for the same wire color and then splice it again. Removing the kick panel cover is a pita, be patient and don't crack its mountings.

 

want to use a marine grade high copper content tinned fine strand wire
to withstand all the flexing and moisture corrosion. that cheap Chinese stuff at the auto parts store aisle is not even worth the time to put in a difficult repair spot such as these.

lay in a stock for all your auto repairs. also has a far tougher water proof insulation

Genuinedealz

 

Sounds like motor brushes are worn down or the rotor is sticking or hitting the magnet in there. I had to replace the plastic gears in one and you have to drill the revit out to remove it. also if the gears good bad some times a big chunk rolls around and stops the motor till you reverse it. make sure you used teflon grease on the gears that come with the gearkit. I didn't once and it takes 5 seconds and it eat them up smooth.

 

Aerocolorado is correct. It goes from the driver's door to the passenger door. So, the problem could be on either side. A good wiring diagram and a volt meter really helps.