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.

David E Bruschi

Porsche likes to use motors as switches building contact points into the motor so it talks to the relay involved ;. headlight motors ,door lock
motor, wiper motors , carry on a conversation with the relays . the motor may have bad contact points or the relay 928 618 104 00 (not on the relay board but behind the tool kit cover as I recall ) may not be working correctly . When you turn off the switch the relay stays energized until the motor says it is in the rest position and it is o k to turn off the power .

Jim Bailey, 928 intl


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


A picture of the rear wiper motor assembly and its contact path to make it stop in its rest position. I was looking for a problem cause and the disk and contacts were fine as you can see, but there were 2 fuses broken., one initiates the 12v power to make it rotate, the timing relay keeps it running for a few seconds, and the main 12v (another fuse) makes it run until it is in its rest position. That is when the contacts on the path break and the wiper motor stops. :