Hey, that's brilliant. You could use the Aeromotive fuel pump controller to run the waterpump, if it draws less than 40 amps.
I passed on the Aeromotive controller due to cost. It's $20 worth of parts that I couldn't justify paying over $300 for. I was originally thinking about the speed controller when I was looking at their huge fuel pumps and was thinking how I'll only be using 5% of the fuel they were pumping 90% of the time. I then found a more reasonably sized in tank fuel pump that wouldn't be such a burden on teh electrical system and cost $450 less than the bigger pump and controller.
If you read past the space aged digital gobbelly gook, the controller is a pulse width modulator that uses the inductance of the motor and a flyback diode. It turns the motor off and on thousands of times per second. The diode prevents the energy in the inductor (the motor in this case) from being wasted as a spark, and the motor sees a reduced voltage, making it run slower. Provided you don't stall the motor, it's harmless and increases the motors life, again, provided you're not running it so slow and bogged down that you're hampering its cooling method.
A friend of mine was giving me grief about the messy disarray my garage is in. My reply was I don't have time to clean during my "stolen moments" in the garage.
And, I have mine idling and revving quite nicely, but I'm on wild goose chases with Marty at Ford Racing as we dance around the leaky valve stem seal issue.(see the 427 burning
oil thread on the small block forum) My Mr gasket material blew out between the primary and side pipe, so I can't use the O2 sensor until I get some gasket material. I'm thinking a sheet of copper and forming a bead around the 4 tubes.