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Boy, I'd rather take a beat down than run a issue on a 68, but. . . If you want to email me direct. I'm looking at a few other questions and then packing it in for the night, but I think I can help you figure this out.
The self power up test on the one link will help you rule out the wiper motor. After that it becomes interesting.
On the firewall side there is a 3 wire plug to the wiper motor. The red should have 12 volts constantly. The brown wire should have 12 volts when the wiper switch is turned on. This wire is what sends 12 volts to the wiper solenoid on the back of the tach. If no power down this wire when wiper switch turned on, most likely the contacts inside the park pawl switch in the motor are not making contact. A quick and dirty way to check is to jumper power from the red to the brown to see if they work.
Welcome to the world of 68 only wiper motors! I learned a lot getting mine to work correctly.