You are correct in that Positive goes to one side of the fan motor from the ignition switch when it is on the run position.

The other wire on the fan motor runs to one leg on the resister block and continues to the HI position on the fan ****. When set on HI the fan **** grounds (connects to negative) that wire. When set on the other positions, the **** sends negative to one of the other legs of the resister block, so that the negative side passes through one or two legs of resister before reaching the fan motor to complete the circuit.