The C3 window wiring is different than anything today.  In newer cars the switch operates a relay.  In ours no relay.  Instead the switches switch a hot lead between up power and down power.  They go to the window motor.  Instead of reversing polarity, they have a seperate ground in the door.  The key here when the door is open it won't work.  When the door is closed the it makes a ground connection.  You lost the ground in the door from the motor to the chassie.   To confirm connect a ground wire from the motor to a good ground  with the door open and operate the window.

When the window goes up it requires more power than going down.  The ground has not Totally failed, but is going bad. 

kstyer, you got me thinking about my driver window refusing to go up all the way unless the door is open.  I have messed with the alignment and think its as good as it will be.  So, its possible the motor is too weak after 40 years.  Does anyone know what the ohm's reading is that a good motor should draw?  Do these motors have a power cut off capacitor when the window is fully up to prevent the motor burning out?

A possible reason that the window does not completely go up with the door shut is the assist spring is getting weak. As soon as the window contacts the weather stripping, it requires a little more force to overcome the friction of the weather stripping. 

The purpose of the spring is to balance out the amount of force the motor has to overcome whether it's raising or lowering the window. 

I should have mentioned that I rebuild the window with new regulator and rollers.  The regulator x-joint was very loose.  the only window part I did not replace was the motor.  the car only has 45,000 miles and the passenger window works great and still has the original parts.  I also took the motor apart and cleaned all the internals, magnets were good, re-greased, ect. I didn't replace the motor due to cost and it was easy to clean, but would if there was a way to measure the motor under upward stress to know if it is weak.

You could try pressing downward on the window with the door closed and attempt to raise it to see if it made a difference in the position of the window when the motor quit.

You could also try doing the same thing on the passenger window to see if that side has more strength.