How to test a wiper motor on my 79

[chrismoore701]

I hooked the wiper motor up in my 79 and only works on high. I bet its the switch, but do not want to waste money.

There are three (3) plugs on it. The park plug, the washer plug and the motor plug. The motor runs on high and parks. I have checked and have good ground. No low speed and no washer pump. Any thoughts.

It does not have intermittent. Just high, low, and wash

Thanks
Chris

[chrismoore701]

I may not have the switch itself grounded in the cab. I have a small 10 gauge wire grounding the cab to the block for now. That will be changed out to a grounding cable tonight.

[chrismoore701]

I just cleaned the ground on the switch to dash connection. And switch plug is grounded to body. Still no low speed or washer pump. Any chance instrument panel not installed could be causing a circuit issue? Any thoughts

[ray_mcavoy]

Here's a quick diagram I drew up showing the connections (and stock wire colors) for the 78 & newer wiper motors:



Fused power is applied to both the motor and washer via the white wire.

For low speed operation, the dash switch grounds the gray wire.

For hight speed operation, the dash switch grounds the purple wire.

When the switch is returned to the off position, it grounds the black wire with the light blue stripe. That in turn grounds the gray wire (through the park switch) which runs the motor on low speed until it reaches the park position. At which point the park switch contacts open and the gray wire is no longer grounded, stopping the motor.

For the washer, the switch grounds the pink wire, and is configured so it mechanically moves into the low position (if pressed when off). Grounding the pink wire energizes a solenoid that pulls in a mechanical latching mechanism that couples the pump to the running wiper motor.


Since you have functioning high and park, it looks to me like the dash switch or wiring is most likely the problem. For testing, you can temporarily bypass the switch and ground the gray, purple, and pink wires on the switch connector as described above. If you can make all the functions work by manually grounding the wires then the switch is probably bad. But if not, look for bad connections in the wiring (most likely in the firewall bulkhead connector or at the wiper motor itself).

[Shugalou]

Wow Nice Ray! I hope I don't have to read this but if I do it's knowing it's just a search away.

[chrismoore701]

Thanks ray. I will try that. I do have a new painless wife harness. But that doesn't mean it's perfect

[chrismoore701]

Ray, that is great. I have two greay wires on my switch and I had them swapped. My painless harness is not so painless.

The next issue is I cant get my washer pump to energize. If I trip it manually it works, but I cant get the solenoid the fire. Is there a way to check this? Do you know the resistance it should have?

Thanks
Chris

[ray_mcavoy]

Originally Posted by chrismoore701

The next issue is I cant get my washer pump to energize. If I trip it manually it works, but I cant get the solenoid the fire. Is there a way to check this? Do you know the resistance it should have?

Yes, you can test the solenoid coil with an ohmmeter. I don't know the resistance offhand but if you get an infinite (open circuit) reading it's either a bad coil or the terminals have some corrosion on them that is preventing a good connection.

[chrismoore701]

I am not sure what the deal is, it works sometimes if I touch the coil wire, and then it will stop so something is bad on the coil. I am going to run with it for now and keep an eye open at the swap meets for a new one.

Thanks guys, just like everything else on this truck, I am becoming an expert on figuring out how everything works