Wiper wont go all the way down when turned off

73 Plymouth with power wash, knob rotates to slow when pushed for wash...
If that description fits ,
Your wipers would stop in mid stroke and reverse the motor to the park position when turned off. Stopping anywhere ould be the park cam on the gearbox, or the switch, and maybe just a loose ground. Check the ground strap gearbox to mounting stud. Good luck
You'll need a page or 2 from a service manual to diagnose it.