Problems with wipers

The wipers on my 70 dart with 2 speed wiper motor stopped working. The wiper motor is getting juice and the switch appears to be working. When I turn on the switch you can hear the motor making noise at both speeds. I checked the linkage and everything appears to be in working order. I checked where the linkage bolts to the motor shaft and it is hooked up. I added an additional ground to the motor and the switch is nice and tight in the dash. (I had a problem with the grounding of the switch on my 72 dart which caused a similar problem).

The Previous owner disconnected the wire that goes from the switch to the the washer pump and wired up his own switch to a new washer pump. Right now there is nothing attached to the terminal on the back of the switch that is designated for the washer motor. Could this cause a problem.

I already tried removing the linkage arm from the motor shaft and then turned on the motor. The shaft of the motor spins at both speeds with the linkage not hooked up.

When a wiper motor goes bad does it completely die instantly or could the motor be getting weak slowly and is now not strong enough to move the wipers under load.

Any help is greatly appreciated.