There is a three wire connector on the firewall that has all three vital signals: power, ground, and the control voltage from the pushbutton controller. Unfortunately the blower controller sits in the circuit between the neg side of the motor and ground. The control signal should get close to 6v at high blow.
If the control signal is getting to 6v and the blower speed is low then the next electrical step is to measure the voltage across the regulator. It should get as low as 1v or close to it. By across the regulator I mean from the negative side of the motor to ground should be about 1v in high blow. To measure this you will have to pull it back apart somewhat.
To make things more fun, we have been made aware recently that one can hook the motor up backwards. When this happens the blower spins just fine but the air coming out is very small. One might think it would get sucked in but it doesn't. It still pushes a little but not much. So if it works properly electrically switch the wires
