One option I'll look into today at work is a opto-coupler. Basically
it is an LED and a detector in the same package, protected from ambient
light. If you wire the diode side in series with the pump, it should be
on as long as there is current going to the pump. What I have to do is
look into hooking up the detector side to the idiot light. I'm assuming
that if the pump fails, that you get an open-circuit condition, (The
windings burn out and break) separating B+ from ground in that leg of
the circuit. By the way, do EE's still use B+ to refer to modern low
voltage power supplies? I build alot of vacuum-tube audio equipment
where we us B+ for the high-voltage DC supply, (~50V to thousands of
volts). I believe the terminology came from the old batteries used to
power early radios. There were tabs on the batteries for different
cells that did different functions, and they were labeled A+, B+, C+.
A+ was a bias voltage, B+ was high-voltage to the tube anodes, and C+
powered the filliments (I may have A and C reversed). Those terms have
gone away, but the B+ lingers on.......
James J
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