1995 Ranger wiper problem

Over the past 3 years, the windshield wipers act up usually at 6-month intervals. While on intermittent, they stop half way up. Have to go to normal or high to get them to move. Turning off, then on won't park them. The wipers act like this for about one week, then total failure. The multi-function switch has been replaced 3 times. Each time, the wipers work fine, then starts acting up again. The high/low relays have been replaced several times. Motor has been replaced once. The GEM has been replaced 2 or 3 times. All work has been performed at Ford dealers. Yesterday, after paying for the $70 diagnostic again, they think it's the motor.
The other electrical problems which Ford says are NOT related: 1. The warning chimes come on briefly for no apparent reason, then stops.
2. The dome light stays on all the time, bulb now removed.
Any suggestions, please. Thanks in advance.

can't garuntee anything but have had similar on other motors and the fault was down to an earth fault. if the earth contact on the chassis is rust contact may be lost occasionaly, try cleaning the the earth contacts,(usually round connecters screwed or bolted to bodywork, there are many of these earth points and could be any one of them)
not always easy to find.
regards brian