I appreciate your looking into this, as I have considering doing the same thing.
The two motors are wired in parallel, so you should be able to follow the yellow and white wire from the motor with 2 wires, back to where they make a connection with a yellow and white from the other motor (though that connection might be sockets to the board, and the connection is on the traces on the board - hard to see). That will identify the power wires for the confusing motor (which has the speed sensor on it). The motor with all the wires has the speed sensor, all of those wires are wrapped together but they do not all go to the same location inside the motor case.
I find it interesting that (perhaps) there are four wires involved with the speed sensor: perhaps two for the emitter, and two for the detector.
Make sense?
