Windshield wipers won’t turn off

[zooklm1]

I have a new opportunity for repair on my 1986 944 Turbo. The wipers won’t turn off unless I turn off the ignition switch. Any positive troubleshooting hints are greatly appreciated!
Thanks,
Lee

[usury]

I had that happen on an 80's Volvo I used to own. It has been a good long time, but I think it had something to do with the electro-mechanical switch in/on the motor that allows the wipers to park after you turn off the stalk switch.

In normal operation, you can turn off the wipers at any position of their sweep and they still return to their parked position. Which means something must keep the wiper motor powered until the cycle is complete. That's the part I'm attempting to describe.

[Zirconocene]

This may not be how the windshield wipers work, but there is an analogous fault in the rear wiper motors on the 944 and, I think, the 928. Or maybe vice versa.

Anyway, the deal is that there's a track with some wipers/spring contacts in the motor. Along the track is a break, which is supposed to stop the wipers unless power is still applied via the switch. What happens is that over time there is enough conductive crud built up that there becomes, effectively, no break in continuity and so the wipers never stop. I hope that's clear.

If you search on RL, there are articles that describe this. If you find something that works, it would be great if you could describe what you did, so that this site can continue to develop as a source for this kind of technical info.

Good luck

[944er]

The way the wiper motor systems work is that they have a continue power function until they reach the park position, then they have a brake function at that location of travel. If the brake function is not working, the motor will coast through that portion of the travel, and re-engage the continue power function. This cycle will repeat until power is removed from the system.

The brake function performed by removing power and shorting the windings of the motor. By shorting the windings, the kinetic energy of the motor is converted to electrical energy (the motor is now a generator) and converted to heat by the resistance of the motor windings. Because if the short circuit, the current flow is very high, the energy is very quickly dissipated, and the wipers stop almost immediately. The quick stop prevents the motor from continuing on to the continue power portion of the cycle.

I'm not familiar with the later cars, but I took a look at the schematic. It looks like the high current switch portion of the brake system has been moved out of the motor, as it was on the early cars, to the wiper motor relay. This was probably a good move on Porsche's part, because it's a lot cheaper to replace the relay than the motor when the contacts eventually fail.

I recommend finding someone with a car that has that relay in it, and swapping yours into their car to see if the issue follows. Schematic says relay G9, but sometimes the schematics have errors, so check by pulling it out and make sure your wipers don't run. Also used in 928s and 911s of the era.

[blueline]

The way the wiper motor systems work is that they have a continue power function until they reach the park position, then they have a brake function at that location of travel. If the brake function is not working, the motor will coast through that portion of the travel, and re-engage the continue power function. This cycle will repeat until power is removed from the system.

The brake function performed by removing power and shorting the windings of the motor. By shorting the windings, the kinetic energy of the motor is converted to electrical energy (the motor is now a generator) and converted to heat by the resistance of the motor windings. Because if the short circuit, the current flow is very high, the energy is very quickly dissipated, and the wipers stop almost immediately. The quick stop prevents the motor from continuing on to the continue power portion of the cycle.

I'm not familiar with the later cars, but I took a look at the schematic. It looks like the high current switch portion of the brake system has been moved out of the motor, as it was on the early cars, to the wiper motor relay. This was probably a good move on Porsche's part, because it's a lot cheaper to replace the relay than the motor when the contacts eventually fail.

I recommend finding someone with a car that has that relay in it, and swapping yours into their car to see if the issue follows. Schematic says relay G9, but sometimes the schematics have errors, so check by pulling it out and make sure your wipers don't run. Also used in 928s and 911s of the era.

Thank you for your input and solid advice on the two electrical issues and also welcome to Carpokes!