My 1987 740T had a bad ground to the wiper motor. The Windshield wiper motor is under a body panel just in front of the windshield, between the hood and the windshield. This panel contains the grill for the heater/aircondition air intake.

Someone had an excelent diagram of the position of the two screws on either side and the bolt in the middle (mine had a ground strap to the rear of the valve cover) that hold this panel in place.

It was a little tricky getting this off as the hood gets in the way at times,and you have to lift the corners and pull away from the fire wall.

Once off you can see that the wiper motor is covered by a molded black plastic cover, and some screeneing to prevent junk from getting into the heater fan.

The wiper motor is attached to a frame that is mounted by two bolts, one hidden behind a rubber plug in the plastic cover. These bolts have rubber bushings,(to reduce noise) and a copper strap is attached to provide a ground path for the motor to the bolt on the drivers side. While removing this bolt, with the key and the wiper switch on, I accidently grounded the motor with the wrench, and to my surprise it started up, and kept on running.

Took the whole assembly off cleaned up the copper strap, and bolts, replaced,
it worked. Put panel back on (getting it into the clips at the windshield is tricky, attached wipers and they still worked.

Next day they did not work. Removed everything again that evening. attached a ground wire to one of three bolts holding wiper motor to frame. Other end of ground wire was attached to the bolt on the drivers side that attaches the assembly to the car. This has now worked for several days. I think the copper ground strap was not making a connection to the motor.

You can test this condition with a jumper cable and the key and wiper switch both on. Ground one black clip to the negative terminal of the battery, and touch the other black clip to the nut that hold the windshield wiper arm. If the the wipers start up then you likely have a bad ground to the wiper motor.

Other than some crip on connecters, (and chiped paint on the edge of the hood) this was a zero $ fix.

Cheers ...........Hugh