I can help a little. The motor assembly is the motor itself and the reduction gear case at the lower end of it. The metal casing of the motor is how the windings in it are grounded, and from there to the case of the reduction gear. The motor has two windings inside, one for low speed, the other for high speed. Both of the wires in the two wire connector to the motor carry 12 volts (more or less) to the motor, depending on what speed the stalk on the steering column is set to. So you should see about 12 volts on one wire or the other anytime the motor is moving the wiper arms. Because the motor uses permanent magnets, you would also see some inducted voltage on the other wire - anytime the motor was moving the wipers. I dont know how much it would be, but it hardly matters what it is. Just dont expect it to be zero or a constant value.
For the wires going to the connector on the side of the reducation gear: One of those wires would have 12 volts going to it anytime the ignition was on. (Its Dark Blue on my 91 *). Thats to allow the wiper motor to 'park' the wiper arms after you move the stalk on the column to 'off'.
The other 3 wires (DB with Yellow tracer, Red, & DB with White tracer - on my 91 *) would each get 12 volts to them at different times, depending on whether you had selected the low speed, the high speed, or the 'interval' from the stalk. The real mystery is what the solid state "Interval Governor' for the wipers is doing. Its hidden up behind the dashboard, somewhere above the fuse box on the left kick panel.
Based on what I see in the forums, that governor seems to be fairly reliable.
If/When my 'interval governor" gives me trouble, I would unbolt the drivers seat, put a sheet of plywood down, and lie on my back looking straight up between the steering column framing and the fuse panel harness, to find the interval governor.
The interval governor is controlled by the stalk on the steering column, and gets its voltage from the same 20 amp fuse labelled 'wiper'.
* Just because the wiring manual for my 91 LX shows the color I listed above, doesnt mean the colors would be the same for all 2nd gen Escorts.
And depending on the year of your LX, the way the stalk works, the wiring to the interval governor and the interval governor itself will be different. On early cars you turn the end of the stalk, on later ones you move the stalk up and down to control the wipers.
I hope you will post feedback on what you find to be the problem; because whatever it is will eventually happen to other people.