Electrical wipers/washer 91 GT

Windshield wipers – how it works theory and operation

Multispeed windshield wiper operation
The wiper motor does not have a resistor pack inside it. It does have one armature brush offset from the other two and a cylindrical permanent magnet instead of a set of field coils. The two brushes directly opposite each other are the low speed brushes. The low speed brush works in conjunction with one of the high speed brushes to provide a second speed.

Self Parking mechanism:
The self parking mechanism is copper circle glued or stuck on the wiper gear. The circle always has 12 volts on it until the wiper comes to the park position. There are two copper spring switch contacts, one provides power to the copper circle, while the other provides a path to the low speed winding. The power contact always provides power to the copper circle except when in the park position. The low speed contact is always in contact with the copper circle. When power is turned off at the wiper control, the 12 volts continues to flow to the low speed motor brush until the wiper blade returns to the park position.


Interval Governor:
The interval governor is a fancy electronic switch that sends the motor a pulse of electricity that varies in duration time. It always runs on the slow speed motor brushes. Turn the wipers on and quickly turn them off. The self parking mechanism inside the motor makes sure that the wiper blades come back to the park position and stop there. The interval governor does the same thing: it sends power to the wiper motor and then turns it off. The duration of the pulse sent to the motor determines how many strokes it makes before stopping at the park position. If you watch carefully, you will notice the wiper blade speed is constant and never changes when you are using the interval wiper function.

Interval governor module


Interval governor location


Troubleshooting:
All tests done with the ignition switch in Run or Accessory position and wipers on.
1.) Look for constant 12 volts on the red wire on the wiper motor. No 12 volts, the fuse is blown, bad wiring or bad connection. This will cause park problems or no wiper operation
2.) Check the ground. No ground and nothing works, bad ground and you get intermittent operation.
3.) No high speed operation, low speed OK. Look for 12 volts on the Dark Brown/orange wire. No 12 volts, bad wiper switch, bad connections or bad wiring.
4.) No low speed operation, high speed OK. Look for 12 volts on the white wire. No 12 volts, interval governor faulty or missing, or bad wiring. Since this is a pulse and not a steady voltage, a test light used in parallel with the voltmeter may be a better indication of operation
5.) Motor low speed test: Jumper the brown/white wire on the interval governor to the white wire. The motor should run in low speed mode. I haven’t tested this yet, so use caution. If the motor does not run, the low speed brush may be bad.

Do all this and by that time, maybe I’ll have figured out some simple tests for the interval governor…

See http://www.popularmechanics.com/cars/how-to/maintenance/how-to-fix-your-windshield-wiper-motors-2 for more help.




Multifunction turn signal switch:
Before you think about replacing the multifunction switch with one from the junkyard, here are some things to be aware of...

The problem is more common in GT models because they had fog lights on the same power wiring as the headlights. Ford undersized the wire and that caused problems.

A word of caution about multifunction switches is in order here. The multifunction switch (high/low beam, wiper, turn signals) are different for different years. 87-98 will work in any 87-89 car. The 90-93 switches only work in 90-93 cars. You can't put an early model switch in a late model car, nor can you put a late model switch in an early car.

Supposedly you can move the pins around to make the switches work in model years that are different from the car the switch came out of. I cannot verify that and haven’t tried it.

Other possible problem sources for the turn signal & headlight malfunction are the ignition switch, multifunction switch and the plastic shell that holds the turn signal wiring connector pins.

The following diagram is for 87-89 model cars.

Turn signal switch wiring:


The following diagram is for 90-93model cars.

Turn signal switch wiring: