Potentiometer on motor for position control
I am trying to get a wiper motor to have a known position 360 degrees around. 


There might be a few possibilities.

First there are continuous rotation potentiometers on the market. They seem expensive though and I can't comment on how accurate they are.

Second, if your device is only ever going to turn through say ten revolutions then go back, you could just get a multiturn pot that will handle that range of turns. (Depends what you're building of course - for example I've heard of servo winches for model sailboats that use this method.)

Thirdly, and I accept this may not be a good answer to your question, but have you thought about using incremental encoders instead? In theory they could be more accurate too. The hardware is quite easy but a bit more programming is required to make these work...