Test a Wiper Motor

Bench testing a GM wiper motor is not very complicated, but, if done wrong, will burn up a previously good motor. Improper grounding can be fatal to the relay or resistor. (this happens quite often by people who attempt a test prior to selling on auction sites. So, they end up selling as "untested" or "for parts" after they see smoke! )

Photos below: showing the connector at the motor, the switch and the motor at rest in it's park position. These are from a 66 Impala but will be the same theory as early sixties through the seventies GM wipers.

I am not showing any info here for GM "delay" systems, though they are similar and can be tested if you are carefull with the delay switch. I also do not show early Corvette systems, but, you can read more at: http://willcoxcorvette.com

A good link for a hidden wiper conversion is here:

http://www.nastyz28.com/2gcog/wipers.pdf

Testing the wiper motor with a spare harness & switch:

Put on some eye protection. Stray sparks, or even some overlooked fluid in the squirter hoses can be a surpr-eyes!

You can test on the bench with jumper wires or a spare switch-to-motor harness can simplify matters. Bench testing off-the-car you will need a 12v car battery or at least a 10 amp battery charger. Less than 10 amp trickle charger is not enough power.

The really important thing is that the switch is properly grounded to the dash frame. There should be a star washer installed on the switch, then it is placed in the dash and fastened in place. The reason for having a solid ground is that the motor relay (inside the motor ass'y, under the washer pump, needs that ground signal to change to the "park mode." A bad ground will let the motor continuously bounce back and forth, also, to continuously run at slow or high speed. Off the car testing MUST be done with a jumper wire grounded to the wiper motor body and also the switch casing for proper "park" function.

This simple bench test procedure will not tell you how much torque a motor is developing, but still is an indicator of a "good" or "bad" used motor. Thus, saving a lot of time R & R'ing wiper motors. You can get an indication of a decent motor just by how it responds to your testing. Turn it on and off. Watch it park. Test the wash/on feature as it cycles and shuts down. Hint: when testing on the car, put a small piece of wet rag under the wiper blade as you test. Then you don't have to keep spraying water on a dry windshield.

The washer pump can usually be fixed with a basic valve kit. Most often dirt from the reservoir gets under the little valves or they simply dry out from old age. Another problem is with the main bellows attached to the piston. Again, they dry out with age and crack. Difficult to locate a replacement, although I have sources if you need one. And they are not difficult to replace. Lastly, the electro-magnetic relay can go crappola on you. Then you have to search around for a very expensive washer pump assembly. Or, contact me for repair.

Sending an original motor out for rebuild is an inexpensive proposition from your local parts store. But, they almost never come supplied with a washer pump attached and quite often you may not see your "original" motor returned unless oyu send it out as a special R&R. And they end up being painted blue or black. Not the original factory finish. Correct restoration goes into the hundreds of dollars. Worse if you have a 'Vette.

On a final note: pay attention to the orientation of the motor link. Upside down is not a good thing. And double check the grounding as you re-install the motor.

Testing the wiper motor independent of the switch:

Keep your fingers away from the drive crank. It will break a finger if it gets in the way.

The depressed park and non-depressed park 2-speed wiper motors (round motor case) can be bench tested independent of the dash switch by making the following connections:

Ground the wiper motor housing.

Connect a jumper wire, minimum 14g wire, from a +12V source (a 10a battery charger will do, but may be inadequate to energize the washer pump with motor running. You will need more amps or use a car battery for power) 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. Full size Chevrolet's had a double connection at the center terminal and other GM's only had one center connection. This is because the vehicle wiring supplied power from different locations. On the car the center 12v terminal is always hot with ignition on.

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. Don't forget to check the fuse. The switch and wiring can be tested with an ohmmeter for continuity of the wire harness. Be sure to disconnect the vehicle battery so you don't fry your ohm meter.

If you do not have low speed the resistor may be burned or broken. Look at it from the underside of the motor. It is under the connector board on the round two speed mpotor. Do not poke at it since they are very brittle with age.

Never apply 12v+ to any terminal except the power terminal. You could burn an internal wire and then be in real trouble.

If the motor stops immediately when switched off (doesn't return to park position), first check the wiper s ground strap. Since the motor is mounted on rubber cushions, it's grounded via a copper jumper strap under one of the mounting screws. This is the ground for the park switch and the parking feature won't operate if the ground strap is missing, dirty, or corroded. The GM wiper motor switch in the dash also requirers a clean ground connection needed for the park position. Very often a dash is painted and the switch does not ground well or the serrated washer is forgotton. 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. Or contact me for more info or how to repair the washer pump.

Testing the coil on the washer pump is easy. Just supply 12v to one terminal and ground the other one momentarily to see if it energizes and pulls the lever. Since OE washer pumps are impossible to find and are expensive, contact me to repair/restore your pump.

Finally, I have some short test videos on Youtube for your amusement.

https://www.youtube.com/watch?v=pdlxLqPTd7A

You can reach my email by clicking on "My Contacts"