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Old 09-22-2010, 12:18 AM
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bad gm wiper motor?

I have the two speed gm wiper motor in my 74 nova. I am rewiring the car and think my wiper motor may be bad. I have run an always hot wire to the middle (hot) terminal and have been testing the motor with a jumper wire that I connect from the hi or low terminal to the chassis ground. The motor runs fine from the top (hi, I think) terminal, but not from the lower (low?) terminal. Then, when I attach the wiper arm to the motor, it shorts out the circuit as soon as I touch the jumper wire to the chassis ground. Is the motor bad or could this be a mis-wiring issue. I metered the wiper arm to the hot terminal and got 00 ohms. I'm not an electrical guy but that would seem to suggest that the motor is being shorted out by coming in contact with the wiper arm, and that is what is blowing the fuse. Is it me or the motor?

Any help would be greatly appreciated - I'm tired of buying fuses while I figure this out.

Thanks,
Chris
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Old 09-22-2010, 04:08 AM
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Actually, what I said wasn't quite right...the system shorts out as soon as I turn the ignition to apply power, whether or not the high/low terminals are applied to the chassis ground. As long as the wiper arm is attached it immediately shorts when the system gets power.
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Old 09-22-2010, 08:45 AM
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If you have the original wiper switch for the car, connect it to the motor and see if it works correctly.

All controls are on the ground side.

Connection wire colors are;
White = ignition on +
PPL = high speed
Gray = low speed
Pink = wash
Case of motor must be grounded.
Black wire on switch must be grounded.

The switch is a special design and works in concert with the wiper motor.
When the switch is turned off the motor will continue to run in the slow speed until the wipers park. When the wipers park, an internal end switch opens and shuts off the wiper motor.
When the switch is in low speed both the PPL and Gray wires are grounded.
When the switch is in high speed only the PPL wire is grounded.

vicrod
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Old 09-22-2010, 09:15 AM
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Thanks for the reply! I believe I have my motor hooked up as you described. The case is grounded, and the positive wire is receiving power at the terminal. This should equate to the "off" position on the switch, correct? If that is the case, I shouldn't be getting a short. I haven't hooked up the switch because I was still testing and I actually plan to use a simple three position toggle switch for the wipers. I was hoping to test one thing at a time but the motor shorts out before I can even connect any ground wires
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Old 09-22-2010, 09:26 AM
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GM wiper motor wiring is not straightforward. High speed is as you would expect - power to one terminal and ground the other. Low speed is a different story, however. GM uses a shunt winding, which is basically a reverse-wound set of wires in the motor. BOTH the High and Low terminals must be grounded to get low speed. The shunt winding partly counteracts the magnetic force of the High speed winding to get low speed. GM did this so that they could use the shunt winding by itself to park the wiper arms when the switch is turned off.
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Old 09-22-2010, 12:00 PM
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Ok, but it still sounds to me like my setup should be working. Does that mean my motor is bad? Can anyone tell me a way that I could meter the motor to tell if it is creating the short? I metered the positive terminal to the ball joint that connects to the wiper arm and got 000 ohms resistance. That equals a short, right?

thanks for the help!
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Old 09-22-2010, 12:54 PM
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Yes, 000 ohms is a short.

vicrod
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Old 09-22-2010, 01:40 PM
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Thanks for the confirmation! I guess I'll be hunting on Ebay for a new one
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Old 09-22-2010, 03:39 PM
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Here, I just found this.
See attached.

vicrod
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File Type: pdf GM wiper-washer diagram.pdf (333.0 KB, 154 views)
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