"Anybody know a way to jumper the motor to test out the two speeds? I tried to decipher the schematics but switch pics have me a bit lost. Right now I'm thinking it may be the switch, but didn't feel like doing the under the dash contortion thing to find out. If I ever get the desired results, I will test the spare motor and offer it and the arms assembly up for sale to one who is in need.

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Yes a couple posts back
but on a 78 maybe the wire colors are different
no matter you can do this
if your connectors are intact separate the connector at the motor
pull the switch to low and on the connector that has the wires going back to the switch shoot for a ground (Continuity)
If you are not familiar with this then set your meter to the lowest ohms setting and touch bare metal with the black lead and the wire with the red lead
when you find the wire with continuity to ground that should be the low speed position--verify by going to hi and back to low and watch it go open in high and continuity in low
now look at where that wire goes on the motor connector. Run a jumper to ground from that wire on the motor connector
Set your meter to VDC and on the connector side check for 12 volts with the switch in low.
You can also shoot the motor connector wires to the top contact on the park switch for continuity to find the power wire.
Now make a jumper to go from batter pos and touch it to the corresponding wire on the motor connector
Now they should run in low---same procedure to find HIGH just shoot to ground at the switch in high to find the right wire to ground
Dont have a meter? well go buy a cheap one! Or in a pinch you could do this with one of your side lights use the ground side of the light to connect to the wire going to ground through the switch for low or hi pos. Then jumper power to the light ---if it lights you have found the wire, if not wrong wire, in this circuit you are not gonna mess anything up putting power to it as long as you dont put power straight to the ground---it has to go through the light!
in the schematic above that would be
motor side connector
LW to ground or battery neg
L to 12 vdc (battery POS)
with those jumpers the motor should run in low
switch the ground to LR for HI
L without the park switch is the power wire
Have a good read on Coolermans wiper science and have a good look at the schematic. Note that park is voltage on both hi and low at the same time and look at the switch schematic the little gray box is the solid metal contact as you move it it connects the posts on top and bottom. all the way left is off, then to the right low, and finally high
if you need it I can give you step by step to shoot through the switch but since it is only happening in low I think you will be good
Hope that helps