The wipers on my 72 operate at only one speed (low I think). How do I get high speed?

I would think you have either a bad switch, a broken wire or a bad motor.

Look at the motor and the connections first. There are 2 black wires. One has a blue and the other a purple tracer. Maybe one got pulled off the motor connector.

If it works at similar speed for both positions of the switch, I suggest you clean and lube the wiper mechanism and the electric motor. You may also make sure the wipers are properly grounded at the ground connection under the dashboard.

If one switch position is just dead, you have an electrical fault, either in the switch or harness.

The wipers work at the same speed in both switch positions. I'll lube the assembly and check the ground wire tomorrow. Thanks

You might also lube the shafts, they can get gunked up.

My shaft always gets gunked up after I lube it.