Posted for "Mark R Steitle" <mark.steitle@austin.utexas.edu>:

 Terry,
 I used two of the GEMS ELS-1100 sensors in my ES, one in each tank.
 They are located so as to activate either a "Left" or "Right" LED on the
 panel when there is 6 gallons of fuel left in the respective tank.
 Basically, they provide a 30 minute fuel warning.  Nice thing is they
 are totally redundant from the EI fuel probes.  They were fairly simple
 to install.  You will need a 5v supply, but that was accomplished with a
 solid state voltage regulator.
 
 See http://www.gems-sensors.co.uk/Level/p37.pdf
 
 Mark Steitle