Mark,
According to the wiring diagrams I have, one of the two small terminals on the
starter solenoid is the trigger. Applying 12 volts to it connects the two large
terminals and the other small terminal together. That other small terminal is
wired to the coil-and-points side of the ballast resistor, and its use is to
provide some extra oomph to the ignition circuit while starting the car. When
the car is running, this terminal is not connected directly to 12 volts. Trying
to run the fan off of it will probably burn out the ballast resistor, kill the
engine because the ignition no longer has enough voltage to fire the spark
plugs, and affect (not permanently or destructively) your tach operation. Or
some combination of the three. If you're going to relay the fan operation then
you can get the high-current supply from the large hot terminal on the solenoid.
The trigger should still come from some ignition-switched (or whatever you
choose) source.
A different note: If the switch is tie-wrapped to the outside of the rad hose
then it will be highly dependent on the airflow around the hose, because the
hose will act as an insulator. Seems kinda hokey to me.
Regards,
Theo
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