I have had 3 Harrison heaters trying to get one with a non-leaking core. They all had just 2 wires. I purchased replacement 12v motors and they just had 2 wires, The 6v and 12v motors looked identical both externally and internally. They both ran on either 6v or 12v, the only difference I could detect was the speed they ran. Doesn't really answer your question. Perhaps your motor is designed to run on a multiple speed switch vs. the original rheostat. If one of the wires is black use it for a ground and test each wire on 12v.
