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I'm hoping that you'll expand a little on the location of that valve
relative to the fuel selector and electric pumps.  

Marv, my fuel lines run essentially straight from the wing tanks through
the cockpit closeout ribs and along the cockpit floor to the center line
just aft of the main spar. At the center line I have connected the L and
R lines to a ball valve identical to the one you use for manual gear
extension. I took the "lever arm" type handle off, drilled and tapped a
3/8 solid rod to fit the male threads on the valve. The rod runs up just
through the top of the console where I've turned it down to accept a
knob. Turning the knob opens or closes the crossflow valve.  Just
outside the console sides on both sides of the fuel line I have a "T"
fitting that takes fuel to the facet pumps mounted just behind the "T's"
and from there, through separate al lines to the header tank.

In the header tank I added two float switches, one at the 2/3 level and
another mounted upside down at the top. I made up a little circuit that
uses relays to automatically turn on a pump (switch for L, R or both)
whenever the lower switch is activated. The pump(s) will stay on until
the upper switch makes contact. These relays WILL fail, so I also have a
feature that gives me a light if the low switch is made and at least one
pump is NOT on. Another light will come on if the upper switch is made
and either pump IS on. A third warning comes from float switches at the
bottom of the wing tanks, if the respective pump is on and there is no
fuel in that wing, I get a light.

I'm no electronics guy, but these circuits are basically simple logic
circuits that I designed in a few hours and built for around 25 bucks.
The electronics weigh maybe 6 ounces, don't take up much room and were
built in a day with RS parts. The only thing that you really need to do
during construction is to put the float switches in the tanks and I
guess that even that could be retrofitted.

If anybody wants the hand drawn schematic let me know and I'll fax or
mail it. By the way, just in case ALL of this fails, I have VM
capacitance fuel level gauges in all three tanks and last but not least
the old sight tube in the header.

Bill Harrelson
harrelson@erols.com
N38BH (85%)