Maybe someone has encountered this problem?

Accessible under the dash are the two wires, going to the passenger door and the two wires going to the driver's door, that are routed to the power window motors in the respective door. +12 vDC to one wire makes the window go up, +12 vDC to the other window makes the window go down.

My problem is that applying power to either of the two motors causes a click and about 1/8 inch of travel of the associated window. The motors will only cause tiny motions up and down with no useful motion. I can see the window roll-up mechanisms twitch during each power application so the motors are producing significant torque. Fresh new fully charged battery power.

An expected culprit would be the screws that hold on the removable door handles....if these screws are too long, they can cause jammed window motion. The screws are removed. No cigar with this cause. Another possible clue, the windows haven't been rolled up or down for maybe 20+ years.

It's hard to see what's going on. Looks like I'll be removing and replacing with new the window roll-up track mechanism...Oh wait...to replace this mechanism.....you have to lower the window.

Just a shot in the dark.......anyone with a guess as to the problem?
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When the C3 was being designed, it appears someone tried to place the fuse panel in the most inaccessible location. Not very imaginative where they put it. I would have placed it on top of the transmission between the transmission and the fiberglass body tranny tunnel. To work on the fuse panel, you'd have to remove the exhaust pipes and transmission. Just a tiny bit more inconvenient than the present location.

 

Did you try to pull the window up manually when you used the switch

 

Because it's happening to both sides the same way, I doubt it's the motors themselves. However, they are fairly easy to remove without disassembling the regulators in the doors to bench check them. They need a good ground through the case to operate -- the two wire connectors provide power for up and down -- so check that their mounting bolts are snugged.

I'm not sure what a failing breaker would do to operation, but there should be one located on the firewall by the brake booster/master cylinder mounting boss. Make sure the connections are firm and test according to this Willcox video:

 

I plan on pulling the motors today. With them gone, I should be able to move the windows up and down manually. I wonder if the +20 years of never rolling the windows up/down has caused something like dirt or rust welding to take place. I''ve bought an all new regulator mechanism so I plan to install that....but first have to be able to move the window down to conveniently remove the old regulator mechanism.

Thanks for the Wilcox ref. I have his circuit diagram.

 

If you remove the motor from the regulator prior to removing the regulator assembly from the door, you'll need to insert a bolt in the safety hole so the spring doesn't unwind suddenly when the weight of the window is removed! A very unpleasant and potential trip to the hospital event should that happen when your hand is up in there.

 

Pretty sure I've an answer to my problem.

I think that some of the metal to metal pivots in the regulator have "rust welded." Also, not much vision into the mechanisms of the regulator, but the tracks seem dry and grease looks like it's hardened. Running a jumper direct from the battery to the motor pins will cause the window to slowly move up and down. Going to now try to squirt some WD-40 into the mechanisms and push and pull on the window to manually help the motor. Now that I know what the problem is, if feel much better about manually pushing and pulling on the window glass as the motor moves.

 

This will be and excellent time to clean off the old hard lubricant from the door locking hardware. I like to use the synthetic lube that doesn’t dry out. Normally there will be broken / missing parts, especially if Bubba previously owned your car. Have your parts catalogs ready. Also, get a powerful small flashlight or two, to light up the area inside the door, it’s a lot easier job when you can see what is going on.