As per a member request, here is an over-view of the GM non-depressed park wiper/washer systems.
These systems were the basic "workhorses" for many years. They do NOT allow for recessed parking (where the wiper blades are pulled down further, past the normal range of sweep motion during proper shut-down). Pictures are typical of 1966 model year equipment.
Please note, this over-view/ testing only applies to the non-depressed park units as shown!
Quite simple to identify with a rectangular motor housing that sticks out from the firewall... This model is a 2 speed unit, with the attached optional washer pump. Single speed units can be identified by not
having the 3rd connection (shunt winding connection) to the far left. Some units have 4 terminal connections, an additional power terminal which is easily spotted to the far right which simply ties into the main B+ connection (as further explained below).
As with any GM wiper system, good ground connections are very important!
These units use a brass strap that is riveted to the motor assembly, and then slipped behind the mounting bushing well. When the assembly is attached to the firewall, the ground connection is then transferred to the motor body. The strap and related hardware must be in place, tight and free of corrosion! Pull apart the bushing hardware for inspection if needed.
The wiring is straight-forward and shown in typical Chevrolet division colors.
These motors have a B+ (power connection) from a switched ignition source---it is "hot" any time the key is in the "on" position, regardless of the position of the wiper switch
A system of selective grounding provides the various functions.
When the wiper switch is.....
The light blue wire and the black wire are shorted together by the in-dash switch. Although they are shorted together, they do not "see" ground via the dash switch.
In LO speed
The light blue wire and the black wire are still shorted together, however, they now "see" ground via the dash switch.
In HI speed
The light blue wire "sees" ground via the dash switch, however the black wire no longer "sees" ground.
activation The dark blue wire "sees" ground for each push/hold of the wash button, although only a momentary push is required as the washer pump then "locks in" for its programmed wash routine. Wash can be initiated in either HI or LO.
During "parking" operation (shut-down) the motor continues to run until the wipers are in the proper position even with the switch off thanks to the internal park switch that provides a temporary ground to the control connections internally.
Bench testing the wiper/washer system
You will need test leads capable of making a safe, reliable connections, a power supply such as a battery charger or car battery, a 10 amp fuse to protect the equipment and some misc. hardware such a 2" #8 machine screw, washers and a nut to provide a ground connection through the ground strap bushing hardware on the motor.
To begin the testing process, wire the "test line" as shown first (shown in light blue), then connect your motor body ground (shown in black) and lastly the +12 supply (shown in red). The test line is simply left disconnected until testing is ready to be performed.
The final connection to be made is to "ground" (or B-) of the power source. The motor will run in "LO" for as long as this connection is made.
Now, to test the HI speed operation, simply disconnect the shunt winding terminal from the test line splice you made (the main connection to ground is still held in place). Once this shunt connection is disconnected, the motor will begin to run in HI and will only return to LO when the connection is re-established. Note to Single Speed Wiper owners, you obviously won't be able to perform this test as this connection does not exist
Now to turn off (test the parking function), you must ensure that the shunt winding connection is re-established. This is due to the fact the motor must be running in LO for it to park properly. This is accomplished by ensuring the control line connections are shorted together once again at the motor as shown.
Once you have ensured the proper connections at the motor, disconnect the end of the test line from the ground source connection. Again, Single Speed Wiper owners need not worry about the shunt (speed control) connection
Depending on what index point the output shaft was at when you disconnected the ground connection, the motor may turn off almost immediately or continue to run for a short period of time until proper parking is achieved.
Checking the WASH function on washer equipped units.
The basic set-up is the same for running the motor in low speed. Please note the additional connections you will have to make to the washer pump terminals.
****Important**** The picture is shown with proper polarity. Some early washer pumps used an electrical means of "locking" in the pumping action after you released the wash button. With these systems, if you don't wire the (+) and (-) connections correctly to the washer pump, you will instantly blow the fuse when you initiate the wash function. These systems used a "polarization tab" on the ground terminal. For more on the polarization tab characteristics, see the "other testing" section below. The units that used mechanical means to lock-in the pump don't require a specific polarity. Follow the picture for wiring if you are unsure of your unit.
A brief touch of the ground connection at the pump will initiate the pumping action. The pump will automatically turn itself off when complete unless the ground connection is left in place OR there is a mechanical issue internal to the pump.
This switch shown is typical of 1966 GM units (Corvair unit shown specifically).
Note the functions are shown in corresponding colors (light blue, black, dark blue) as they would be connected with the wiring. Please note the polarization tab. GM used terminals that had a small "tab" protruding to prevent incorrect indexing (keying) of the wiring connections. This tab prevents seating a harness connector(s) on fully/correctly to prevent wiring errors.
You can use a basic ohmmeter to see if you have continuity (a through connection) or an open (no connection) from the body of the switch to each terminal at each appropriate setting of the switch.
Speaking of the body of the switch, just like the motor itself, the switch needs a good dash ground for proper operation. Make sure all ground straps/mounting hardware is in place, clean and tight.
To check the integrity of wiring under-hood with the switch still mounted in the dash, you can use a simple test light. Having an assistant in the driver's seat makes testing much easier. Begin by disconnecting the wiring harness from the wiper motor (and washer pump if equipped). (Each step in the sequence assumes the previous step worked properly).
-Connect the test lead of the test light to a good clean metal ground. Have an assistant turn the key to the "ON" position (just before start/crank). Use the probe end of the test light to touch the terminal of the yellow power supply wire. It should light up. When the key is turned "OFF", the light should go out. If there are (2) yellow wires tied together as shown with the example motor, either can be used.
-Now take the test lead of the test light off of the ground connection you previously made and clip it to the terminal of the yellow power supply wire.
-With the key "ON" and the wiper switch "OFF", touch the test light probe to each remaining wire. The light should NOT come on.
-With the key "ON" and the wiper switch in "LO", touch the test light probe to the light blue wire and then the black wire. Both wires should make the light come on.
-With the key "ON" and the wiper switch in "HI" touch the test light probe to the light blue wire and then the black wire. The light should come ON with the light blue wire BUT NOT WHEN TOUCHING THE BLACK WIRE TERMINAL.
-With the key "on" and the wiper switch in LO OR HI, have the assistant press in and hold the wash button. The light should come on when the dark blue wire terminal is touched. The light should go out when the wash button is released.
Incorrect operation or specific non-functioning operation determined by testing can indication bad switch connections, a bad switch, incorrect wiring (not properly indexed on the swtich itself) or bad wiring or poor connections between the dash and motor connections. No power on the yellow line can indicated bad wiring, poor connections between the dash and under-hood, a blown fuse or ignition switch circuitry issues.
This "Guide" should at least get you started down the correct path!