[Jimbobeast]

Gentlemen,
I have a question and I believe I know the answer but I am so frustrated that I just want confirmation.
On Oct 11, 2021 I bought a new wiper motor/pump assembly from APE. It was a ROYAL PITA to attach (that was a separate post) and now that I have all the harnesses installed, it does not work. My switch is making good ground. I have 12V power at the middle terminal on the motor and the two black wires make good ground when the switch is alternately on high or low. That's what it is supposed to do, right?
I ran jumpers from the battery terminals to the motor - still no life. So, in my non-electrically astute mind it has to be a bad motor, right?
Looks like I'll be buying a new motor. I can't expect APE to accept a return after all this time, even though the motor has never run. I did not think to bench test a brand new motor.
Anything else I should do to further test, or any other easily remedied fixes I should try?
Also, this is a 1970 GTO convertible with concealed wipers. But you probably knew that.
Here is a photo of the terminals (I don't know why I am posting this photo) and one of Oscar the GTO puppy - Supervisor of Restoration

[Peter Serio]

One thing about any of those 1960s, 1970s era wiper motors is that they are noisy. So much so that GM decided to mount the motor to the firewall using 3 rubber bushings. There is a need for the wiper motor's exterior metal outside casing to be grounded to the body of the car. (This would be in addition to any of the plug-in wires.) That is the first thing I would check. There is one flat copper ground tab that overlays one of the bushing mounts, right where the bolt goes thru. Is your ground tab intact?

[Jimbobeast]

Peter, that makes perfect sense. I'll check.

[Jimbobeast]

Well...good thought but the grounding strap was in place. Just in case it was not making a good enough ground, I also grounded the case directly to the battery (-). Still nada, not a spark of life. So close...

[Jimbobeast]

Actually, in the photo above you can see the grounding strap to the right of the terminals.

[Peter Serio]

One problem that I used to see often at work (& this was in the 1980s) was that the GM wiper motor's armature would stick. Two things can make it do that: 1) was a dry oilite bushing on one or both of the shafts, that or water from the cowl seeped into a bushing over the winter.) #2 would be no current getting to the wire windings on the armature.

This would usually happen a on motor that was sitting for some time, never turned on. The cure was to lube the bushing(s) and then carefully remove the brushes and clean both the commutator and both brushes. To clean the copper commutator I used a eraser; they made a special one for model trains. To clean the rails on the tracks.

To clean the brushes you want to use a small piece of sandpaper, that or a tiny jewelers file. Keep in mind that the brushes are spring loaded. It could be a weak spring or a stuck brush.


Here is what I use:

[Jimbobeast]

Well, I got the new motor today, ran out to the garage and hooked up the harness without removing the old motor - still nada. So, I just went through the diagnostics again and now I only had 0.5 volts at the middle terminal. Back under the dash and sure enough the fuse was blown. I replaced the fuse with a new 25A unit and bingo, 12 volts at the middle terminal. I plugged the harness into the old motor (still on the firewall) and now it works like a charm - low, high, pump and retracts the way it should. I ran it for a couple of minutes without incident. I had 12V at that terminal last week. I even ran jumpers from the battery (+) and (-) directly to the motor with no go. I don't understand all of the above, but I know my wipers are now working and I am a happy camper. Thanks for all the advice, Pete.