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F150 windshield wiper problem

I just bought a 1999 Ford F150 and discovered on the first rainy day that the wipers only turn on when the car is in neutral or park and once on they do not turn off unless in park or neutral which means they stay on when driving and cannot be turned off unless I stop the truck. I have cleaned out the switch but that did nothing. Any ideas?

Because the problem is related to where the shift lever is positioned, there may be a problem with the PRNDL(prindle)switch. This switch tells the computer what gear the vehicle is in. There’s a history with Ford vehicles that when this prindle switch malfunctions it can cause all sorts of wierd electrical problems.

Tester

Looking at some data it shows the wipers are controlled through the GEM module. Make sure the wiper switch is connecting properly. The data doesn’t show the switch itself and how it is tied in the circuit.