Rear Wiper Motor Service

Rear Wiper Motor Service

>My rear wiper dosen't sweep. I've replaced the switch, but nothing happens.

I think there's an inline fuse back by the motor. Check that first.

First thing, take a VOM and make sure that you have voltage at the rear wiper motor. (This might be a two person operation, 'cause once you push the wiper button, it is a timed switch, running the wiper for three swipes or so... at least it is on my car.)

Then you might want to try removing the rear wiper motor, open the gear case, and make sure that the contacts inside are clean. While you have this open, you will also probably want to re grease the gear case as the old grease has undoubtably turned to something that is anything but a lubricant. If it still doesn't work, then your motor made be pooched. I've opened the wiper motors and rebuilt them on occasion, but if it is badly burned, you are better off buying a new rear wiper motor.

[TIP: Brown wires are GROUND wires in Porsches.]

J.B. Lisankis
1981 928 S Euro Spec 5 Spd

David E Bruschi wrote:
>Can anyone tell me, how the rear wiper knows where to park it self? My
>motor and switch seem to work fine, but the wiper usually goes across a
>couple times, three I think and then stops wherever it feels like it. To
>combat this I cycle the wiper a couple times and then by pure luck it ends
>up back on the left side. A minor issue but frustrating none the less.

The rear wiper momentary switch energizes the electronic control inside the rear wiper relay (mounted next to the wiper motor). This energizes the relay contacts, which turns on the rear wiper motor. After about two or three seconds, the rear wiper relay turns off, removing the power that it furnishes to the wiper motor. There is a separate power supply directly to the rear wiper motor thru fuse #18. Inside the wiper motor, there is another set of contacts, operated by the wiper drive mechanism. These contacts connect the separate power supply to the wiper motor. The contacts are closed except when the wiper drive mechanism is in the park position, so if the wiper is away from the park position when the relay cuts off, the internal contacts furnish power to run the motor until the wiper gets to the park position. At that point, the internal contacts open, and the wiper stops.

In your case, it sounds as if fuse #18 may be bad. If not, the internal contacts may be bad or misadjusted.

Wally Plumley
928 Specialists

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