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Electric Wiper Switch Replacement |
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billd
Moderator Group Forum Administrator Joined: Jun/27/2007 Location: Iowa Status: Offline Points: 30894 |
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AMC and Ford shared wiper switches and motors only 1973 and later. Prior to that, Prestolite supplied the entire wiper system including motor, mounting plate and wiring harness. The motor is a unique compound wound motor up through 1972. After that, Motorcraft supplied permanent magnet wiper motors (in the early 60s Ford used Prestolite wiper motors as well, single speed. I have one of those motors from a 62 I believe. Model number prefix is EPW) The speed of the Prestolite motor is controlled by inserting resistance into the shunt field winding to reduce current through the shunt and increase speed. I know that sounds counter-intuitive but a series wound DC motor will run away. The shunt, or parallel field slows it down and controls speed. More power to the shunt field winding, less speed, less power to the shunt, more speed. So the switches up through 1972 have a resistor. For high speed the shunt is powered through the resistor. For low speed, they feed the shunt directly to slow it down. Some cars from AMC got 3 speed wipers - the motors are basically the same, the SWITCH is different. It will have two resistors hanging off the back. Low, medium, high speeds. Low goes through higher resistance (both resistors) medium goes through one resistor, high is direct, no resistor.
You cannot use a Motorcraft switch or mist control on a Prestolite wiper motor. |
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Nardo
AMC Apprentice Joined: Dec/21/2010 Location: United States Status: Offline Points: 174 |
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Great explanation, thank you. I really couldn't figure out why a generic switch would not work but now I (mostly) understand it.
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Mike
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