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My system is not yet completed, but I thought I would throw the idea to the
list.  The system is of the same concept as the fully automatic one
described below, but instead of floats or optical sensor, it uses a
capacitance gauge.  The capacitance gauge is DESIGNED to send a fuel level
reading to a gauge, and ALSO to send a low and high warning at any preset,
user-defined level.  It has dedicated wires to send the hi/low fuel signal.
I am using the low fuel signal to turn on my pumps.  It will be calibrated
to turn on at about half tank and turn off at full.  It will also send the
level to a panel mounted gauge.  One instrument, fully automatic.

Since nothing is perfect, what is the caveat?

Capacitance gauges are rendered useless by the presence of water.  The
highly accurate senders will pass a false "full" reading if water is in the
tank (because water is a better (worse?) conductor.  So, how keep it simple
and safe?  Now it's not quite as simple, but will have a second sender
mounted in the tank that will just light a warning light if fuel drops below
the 1/2 level, at which point I can manually override the automatic system
and turn the pumps on.

It may not be KISS, but I do have
1. redundancy in monitoring of the fuel level
2. always have a minimum of 1/2 header tank fuel level
3. a fully automatic system with override ability.

Love to hear your comments,

Matt

P.S. - my fuel will draw from the wing tanks with the standard Facet pumps.
They will be inline for redundancy, and the wing tanks are linked together
with a T-fitting.  I know I can't control weight/balance that way, but I
don't think I really care.  They should be more or less equal at all times.
My wing fuel level will not be measured, but I have a totalizer to tell me
how much fuel I have burned (using the VM1000 and EC?).  I will also have a
panel light to tell me if I have a fuel transfer pump failure.