hi all. I have a truck that was originally a 77 3\4 ton that was
equipped on the dash for dual tanks (with the switch)..when i got the
truck it only had one tank on it. I've since changed the 77 cab to an 81
and this cab also has the switch for dual tanks. I've determined that
the sending unit in the tank is defective by using a ohm meter and
temporarily run a jumper to by pass the corroded center pin strap on the
lower section of the sending unit and now get reading on my meter..i'll
replace the sending unit but have it like this just to try and get my
fuel gage to read something other then way past full (3 oclock
position)..The wiring under the truck is a rats nest for the fuel
sending unit and am trying to trace out what is what. I'm only ever
going to have one tank on this truck. The wires in this newer cab seem
to go to a relay of some sort located beside the main fuse block then to
the switch on the dash. I go under the truck and can't seem to get
voltage on any of the wiring for the sending unit (s)..My main questions
i guess are 1.) whats this relay between the switch and fuse panel and
could it be defective? 2.) what voltage should the sending unit be
getting? 12v or a lower voltage that comes from that relay. In the
meantime i'll pickup a new sending unit but also trying to have the
right voltage\wiring ready.. the original wiring harness\fuse panel from
the 77 used glass type fuses and the new cab has push in auto fuses.

advice would be very helpful..

confused as hell, Jeff