>I have a sender unit I need to check before I install.  How to check?

The fuel gauge sender is a variable resistor.  As the float floats up and
down in the gas it moves over contacts that send varying amounts of
resisatance to the fuel gauge.  To test connect a voltmeter to the 2
contacts on the outside  of the sender and measure the resistance with the
buoy at different positions.  I'm not sure of the values but someone has
recorded them and they are either in the message archives or ftp section of
vanagon.com.  If you don't have access to a voltmeter you could even
connect the sender (out of the tank) to the gauge, turn on the ignition and
move the bouy and arm up and down and see if the gauge responds.

Hope this helps,

Andrew Fox
Looking to buy a gasoline heater.