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Electric Wiper Switch Replacement

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billd View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Jan/19/2022 at 3:34pm
Originally posted by Nardo Nardo wrote:

Originally posted by Trader Trader wrote:

Have a look:
Believe AMC and Ford used the same sources for wiper and light switches - theory that cannot be proven!

Hmmm, that is pretty interesting. I have a rebuildable AMC wiper motor and plate but I also have a second AMX with vacuum wipers I'd like to convert. For this car I'm not stuck on originality and I would not mind experimenting with a conversion like this. Electric wipers have been one of the harder group of parts to put together. 

There was also a comment about 69 having a two speed switch. My switch is actually from a 70, as is the dash I'm using as a base for my custom dash install. Is that 2 speed or variable? If I have to, I think I can salvage the switch, I'll just have to figure out how to extend the broken shaft. 

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Nardo Quote  Post ReplyReply Direct Link To This Post Posted: Feb/02/2022 at 4:38pm
Originally posted by billd billd wrote:

Originally posted by Nardo Nardo wrote:

Originally posted by Trader Trader wrote:

Have a look:
Believe AMC and Ford used the same sources for wiper and light switches - theory that cannot be proven!

Hmmm, that is pretty interesting. I have a rebuildable AMC wiper motor and plate but I also have a second AMX with vacuum wipers I'd like to convert. For this car I'm not stuck on originality and I would not mind experimenting with a conversion like this. Electric wipers have been one of the harder group of parts to put together. 

There was also a comment about 69 having a two speed switch. My switch is actually from a 70, as is the dash I'm using as a base for my custom dash install. Is that 2 speed or variable? If I have to, I think I can salvage the switch, I'll just have to figure out how to extend the broken shaft. 

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.

Great explanation, thank you. I really couldn't figure out why a generic switch would not work but now I (mostly) understand it. 
Mike
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