Jack Houpe
GT40s Supporter
I made a comment of the wiring of SPF cars. One of the issues that I found inadequate was the circuit for the blower motors. If you look at the wiring diagram and follow it out it uses no relays to control blower motor current. It all goes through the ignition switch which then feeds the blower motor switch which uses a combination of resistors to change the speed of the blower, this is ok BUT the wire size is undersized for amount of current of the total circuit and the switches are undersized. Example I noticed that when the blower motors (2 of them) were on high and came to a idle with my car the blower speed decrease considerable. After pulling my switch panel off I noticed the main power feed to the rotary switch (blower speed switch) and the wire going to the HIGH position to the blowers to be brown from excessive current draw. I replaced the terminals and did not pay any more attention to it. During my open road race I had the fan on high while driving the event with the AC off to keep cool in SW Texas. After the event I went to turn my key switch off and it was hot to the touch. This concerned me so after returning home I looked at the circuit overall and found that the wires going to the blower motors are much smaller than the wires from the motors to the plugs on the harness. The motors draw 8 amps each or 16 amps total on high, the keyed switch is rated at 15 amps max, I am sure the switch on the dash is rated for even less. Overall the wire size and switch size become resistive under high current draws. The correct fix would to be replace the wires going to the blower motors with a larger size and to use a relay to feed that circuit and not have all the current go through the keyed switch. I elected to use a PWM (pulse width modulator) to control the speed of the motors doing away with the rotary switch and replacing with a rheostat and running new wires to the high (orange wire on the blowers) side of the motors. I also used a relay off the keyed switch to control the current of the motors and a auto reset breaker for protection. This system works very well and there is a noticeable increase of CFM at idle and under way. The PWM are less than $30 on ebay but all this will require some soldering skills and wiring of the correct size. Mike Trusty and Kirby Schrader have also done the same with there cars with the same success. The diagram attached is for the circuit which I have described. The relays in the circuit are NOT for the blower but for the small servo motor that reverses for the recirculate servo motor.