Check this thread https://www.airforums.com/forums/f45...cs-187676.html
I had a similar failure to yours. When I removed the cap with the level, there was a square tube I could turn with a 7/16 socket on an extension, it is hard to turn when under load.
My problem was the ground connection which goes through the jack tube to the frame. I had to remove the jack to clean up the frame and mounting plate and I replaced the bolts and star washer under the mounting plate.
Since you replaced the switch, you know how to take the cover off. Apply 12 v to the input line and ground directly to one of the bolt heads on top of the drive unit. If the light comes on when you throw the switch you have made the proper connection. If not, check for a burned out bulb or loose connection to the light.
If the motor spins when you toggle the switch, then you are good on the jack - check the ground connection.
If the motor does not spin, take the red and black wires off the center blades on the side of the up/dn switch and connect directly to 12 v and ground (I used a battery charger for this since it can protect itself from a short circuit). If the motor spins, it is good. If it does not, Time for a new power head.
My unit had three switches, the up/down toggle and two limit switches under the cover. There are multiple connections and many of them were loose, or corroded so check, clean and adjust everything while you have the lid off.