'72 Wiper parking and washer troubleshooting (1 Viewer)

[steffan]

As I continue to troubleshoot my new build new issues come up. During the rebuild, I completely disassembled the wiring harness, traced out all the wires, replaced bad etc. With the help of Coolerman's post, website and wire diagrams I was confident everything was good to go.
That being said, I tried the washer the other day and nothing happened. It was a pretty sickening feeling since the harness is now wrapped and tucked away under the dash.
Long story short - With so much of my attention going to other parts of the harness, I didn't pay enough attention to the actual workings of the wiper system.

LESSON: the wiper system works though a switched ground, not switched power as most 'modern' systems. Verify your grounds

 

[steffan]

starting with the washer, I took the switch out of the dash and confirmed all the leads - everything was wired correctly.
for the washer (someone please correct me if I describe this wrong) the power comes directly from the fuse panel to the squirter pump. from the pump the negative lead goes back to the switch - when you turn the knob to activate the switch, you are grounding/ completing the circuit.

This is where my issue was: when I painted the body, I was proud of myself for getting a good, thick coating of epoxy primer and paint over every nook and cranny including the back side of the dash: the switch was not grounded.

here is how it looked from behind the dash ( I had already started trying to remove the paint at this point)

 

[steffan]

now that the wiring/ switches were all in along with the heater access to the backside of the dash is minimal - barely could get my had back there.
I found a shoulder bolt, self adhesive sand paper and drill.... placed the switch and everything worked

 

[steffan]

Part 2 - the windshield wiper park function.
Again, thanks to coolerman for the write ups - couldn't have done it without them

Wiper Wiring Science

When I was putting everything together, I think I was so relieved that the wipers worked at all, I overlooked or wasn't worried that they didn't park themselves.
I double checked the wiring and it was correct so I started looking at the park switch on the motor. I had disassembled everything to clean/ inspect it as well as re-solder the wires on the plates.

here is a great description of the operation by coolerman (from the page above):

The park switch is located on the front of the motor housing. It is a simple three contact switch consisting of three thin copper arms separated by a series of insulated spacers. Two of the arms are fixed (the top and bottom arms) while the center arm is movable by the park plunger. This plunger rides on the main drive gear. There is a ramp on the gear that causes the plunger to rise up once per revolution of the gear forcing the middle contact against the upper contact. The center arm is normally down 90% of the time. When down, it makes contact with the lower arm, effectively grounding the center contact. This is why you MUST have the windshield grounded! the Park function will NOT work if you have a bad or poor ground!


I've looked a bunch of different threads on this and they speak to it but never really go into detail on he order of the plates.

There are 3 insulation plates and 1 metal plate - the order is critical as well as the spacing of the arms. Hard to see but next to the housing is the metal plate, followed by a short arm with thin insulator. Next is the long arm with a thick insulator. Finally, another short arm with thin insulator.

 

[steffan]

here you can see the switch while the wipers are functioning: the plunger is down and the bottom/ middle plates are touching.

in the second picture, you can see the plunger protruding up, pushing the middle plate up, contacting the upper plate and 'parking' the wipers

Coolerman does and excellent job describing the science behind it on his page.

Hopefully, these additional pictures will help someone in the future

 

[steffan]

here is a picture of the switch/ wires for reference. the front of the switch is the ground surface to the dash. when you turn the knob, it rotates the cam over to contact the blue yellow wire (coming from the pump) to the dash, completing the circuit

 

[Engineer8000]

Nice write up. I would mention a couple other quirks with the wiper circuit. There is a wire swap at the 4-terminal connector at the wipers. Also, that 6-terminal connector at the switch is keyed to only fit the switch one way.