A post by LocDoc on the 67-72 truck forums
I am posting this in a new thread so it can be added to the FAQ section. It is instructions for testing the wiper motor out of the vehicle. I made up some jumper wires with spade terminals and/or alligator clips to make the hookups easier. Watch out for the rotating arm when you make the connections, it can wind the wires up pretty quickly…… The 2 speed wipers are about half way down.
Article from Ray’s Chevy Restoration Site
Q – How is the windshield wiper motor wired ? How can the circuit be tested ?
A – Single speed wipers were base equipment on most early 60’s GM vehicles. They have one (fused) power wire that is connected directly to the wiper motor. This wire is live whenever the ignition switch is on. A second wire connects the motor to the switch on the dash. When the wiper switch is turned on, it completes the circuit to ground (the dash). The single speed motor can be tested using the following procedure:
* Use a test light (or voltmeter) to check for power at the wiper motor. Do this with the ignition switch on (wiper switch can be on or off). No power at the motor is an indication of a bad fuse and/or wiring.
* Next, (with the ign switch still on) connect a jumper wire from the switch terminal on the motor to ground. That should cause the motor to run. If it doesn’t then the motor is probably faulty.
* Finally, the wiper switch can be tested with an ohmmeter or continuity tester. Also make sure that paint or corrosion isn’t keeping the switch housing from properly grounding to the dash.
Two speed wipers with washers were available as optional equipment on early 60’s GM vehicles. They became standard equipment in 1965 or 1966. This system still uses the same basic wiring principles as the single speed wipers. There is still a power wire that feeds the wiper motor whenever the ignition switch is on. Except now there are three wires going to the switch. The switch grounds one wire for high speed operation. Two wires are grounded for low speed operation. The third wire grounds the washer solenoid to activate the washers. Note that many ’75 and later vehicles used a small electric washer fluid pump mounted to the reservoir instead of the older wiper motor driven pump.
2-speed wiper motors
There are also 3 types of 2-speed wiper motors. One is a non-depressed park motor that is easily identified by its rectangular motor case. Another is a depressed park motor that has a round motor case attached to the gearbox at an angle. The third is a permanent magnet motor that has sort of a rounded 6-sided motor case. The diagram below illustrates the non-depressed park (rectangular case) motor. The washer has been omitted for clarity. The depressed park (round case) motor uses the same wiring concept except the terminals on the motor are arranged in a different order (3 Low, 2 Power, and 1 High). The permanent magnet motor (used primarily on 1978 & newer GM pick-up trucks) has separate terminals for the park switch and therefore uses a different wiring setup.
Testing the wiper motor independent of the switch: (in or out of the vehicle)
The depressed park and non-depressed park 2-speed wiper motors can be bench tested independent of the dash switch by making the following connections:
* Ground the wiper motor housing.
* Connect a jumper wire from a +12V source to the #2 (Power) terminal on the wiper motor. It’s the bottom terminal on the rectangular motor or the middle terminal on the round motor.
* Connect a jumper wire from ground to the #1 (High) terminal on the wiper motor. It’s the middle terminal on the rectangular motor or the bottom terminal on the round motor. This should operate the motor at high speed.
* Leaving the above connections in place, add an additional jumper wire between the #1 (High) and #3 (Low) terminal. #3 is the top terminal on both the rectangular and round motors. This should operate the motor at low speed.
* On the rectangular case motor, leave the jumper between terminals #1 and #3 but disconnect it from ground. That should cause the motor to run (at low speed) until it reaches its park position at which point it should stop.
* On the round case motor, leave terminal #3 grounded but unhook the ground jumper from terminal #1. That should cause the motor to run (at low speed) until it reaches its park position at which point it should stop.
If the motor operates normally in the above tests but not when installed on the vehicle then the problem is most likely in the switch or maybe the wiring. Also, the switch has to be grounded to the dash or the wiper will not work. Don’t forget to check the fuse. The switch can be tested with an ohmmeter.
If the motor stops immediately when switched off (doesn’t return to park position), first check the motor’s ground strap. Since the motor is mounted on rubber cushions, it’s grounded via a copper strap attached under one of the mounting screws. This is the ground for the park switch so the parking feature won’t operate if the ground strap is missing, dirty, or corroded. If the ground strap checks out okay but the motor still doesn’t go into park then the problem is most likely a worn out or dirty park switch. The park switch is located inside the motor’s gearbox so some disassembly is required to check/clean the switch. I recommend consulting a good repair manual for the motor disassembly procedure.