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Wiper circuit

Mach1 Driver

Mach1 Driver

Well-Known Member
Donator
Could someone check my work please? I couldn't find a coherent description of how the wipers work, so I drew-up a schematic based on the wire diagram (what the hell- boy is that useless??) and guessed at the operation. The switching didn't make sense so I guessed that the RUN position of the motor switch must cycle to PARK when the wiper blades are down.
Thanks
 

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I've never been able to fully understand the wiper system myself, particularly the 67/68 foot pedal washer system. Don't forget there are one and two speeds. Could you identify wire colors? I know the colors changed from 64.5/66 to 67/73.
 
That looks right from a functional view. What that implies is that there is no high speed with the 6768 foot pedal.
 
Wellll that's what ya get for having a pre 69;)
I have no clue what the earlier cars do, since my manual is for my 69.
What I really need to know is if the motor position switch is in "park" when down, and "run" at all other times. If that is correct then my schematic is correct.:eek:
 
The 70 shop manual has (looking at the switch from the motor side) has continuity between orange/white and red, and white and black when parked.
Low speed has continuity between orange/white, red, white
High speed has continuity between orange/white, red, blue.

By Jove, I think he's got it!
 
Thanks Mid, that comes from the wiring diagram, but what it doesn't tell me is this:
is the motor position switch in "park" when the wipers are down, but in "run" at all other times?

If someone can tell me that, then I know it is correct.
 
I have no idea. Have you consulted the Shop Manual, which often has tests for motor functions?
 
A member from another forum provided a correction. The FORD drawing shows the switch in the motor as SPDT with the Park contact grounded. It didn't hurt anything but it was superfluous and I couldn't understand why it was there. Well it turns out its really a SPST, and the FORD drawing is wrong.
Please see the attachment.
 

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This is the straight scoop, the real deal, the unvarnished truth, the real skinny, and gospel. I know “how” and “why” the wiper circuit works. I think you’ll find this surprising. There is real science going on here.

I have received so many versions of how the wiper circuit functions (from 3 forums) that I still had doubts. So I took the perfectly good wiper motor out of my completely stock 69 Mach and investigated. BTW, I’m the original owner so I know its completely stock. I disassembled the motor and found that it agrees 100% with the FORD diagram (printed by Helm).

I had misgivings about the diagram because the Park to chassis contact in the motor seemed superfluous. I disconnected the park contact, reassembled the motor and hooked it up to the car.

Some background: the motor has a SPDT switch that is in Park for about 15 degrees of its rotation. The rest of the time this switch is in the Run position.

It is important to note that stopping is a two stage process, and stage one occurs when the circuit is switched off via the dash switch. The motor is prepared to stop by switching it to LO for the remainder of its rotation. A slower motor is less likely to coast too far.

I started the motor but when I turned the dash switch off the motor wouldn’t stop spinning. The Run switch would open and you could hear the motor turn off, but it would coast right through the 15 degrees until it switched to Run and started going again. It did this repeatedly, every time tested.

I wondered why this was happening and a light bulb went off. I looked at the schematic to verify and confirmed my suspicion. Both Park switches close, connecting the ends of the motor coil together. Without this connection the motor would never stop, at least not within the allotted 15 degrees of rotation.

So here's what happens: when the motor is turned off, the magnetic field in the motor coil collapses causing a reverse voltage, called a Back EMF. Connecting both ends of the coil together causes the motor to “reverse” for the instant that the magnetic field is collapsing, and the motor stops before coasting into the Run position.

I reconnected the Park contact in the motor and it operated normally, stopping when it should. Isn’t that cool? It momentarily puts on the brakes. Betcha didn’t see that coming! Please see the attached operating sequence.
 

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Those analog electrical engineers were pretty savvy in their time, weren't they?
 
A member of another forum read my description of the motor brake and said it's a well know technique among permanent magnet motor people and is called Dynamic Braking. Who knew?
 
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