I can tell you what I had to do with mine was take it completely apart, what I found was it was just gummed up, there is a leather "flap" that runs the half moon shape in side as the vacuum pulls it from one side it switches it to then pull vacuum from the other causing it to go from side to side, if the switch does not actuate easy that is where I would start, you may not have the valve opening and closing causing no vacuum to enter the sealed chamber. Just take it apart you will see how it works.
Another thing to do is run a thin coat of vasiline around the paddle . This will make the rubber swell a might within the "U" shaped chamber . scrubba
There is a company that has ads in Hemmings that rebuilds them. If I remember right a tri 5 electric will bolt on.
You are not understanding the switch part...the knob and cable just move the actual switch, which is the lump on the top of the motor at the end of the cable. Vac line from engine hooks to the nipple on the side of that... To start your analysis, put a bit of oil on the cable and on what it moves on the motor...maybe WD 40 first, just to get it seeping into things, then some real oil once parts are free. Next, put some light oil like 3-in-1 into the nipple, work motor back and forth by the linkage arm facing the camera. If everything moves and motor emits gasping sounds as it goes back and forth, try hooking it to a vac source and see what happens.
finally got a chance to pull it apart. It was all gummed up. Wouldn't even turn by hand, cleaned it up put it back together now I have one way vacuum so the wipers will go fully one way but then stay. there was only one vacuum line hooked up to it looks like one should also go to the diaghram the one that was hooked up was on the inlet side
the other port is just a vent. there is still a valve sticking, go back and do it agagin. there is a valve that opens and closes and forces the piston back and forth.just like a milking machine, sucks it one way, then sucks it back again.