I have a 1989 F350 Diesel 7.3 V8 with dual fuel tanks...it is not a standard truck in that the chassis is a 10 ft flat bed. Here's my problem(s)

- The fuel gauge does not work in either tank - it reads full at all times and when I switch tanks it will not send fuel (it will not pick up fuel from the rear tank)

I've been told it might be the sending unit or selector valve BUT I can't find either part at Advanced, O'Reillys, Autozone or Napa - they look up the year make and model and I've ordered 3 valves because they said they would fit but they don't....can ANYONE please offer me some advice & assistance at where to look for the part(s)?

Am I on the right track and where can I find the parts? I've searched Amazon & Ebay but I'm not sure I'm calling it the right name, etc. I would so appreciate any help anyone can offer!

 

welcome to FTE.
your problem could be the fuel selector valve, bad pickup tube in the rear tank, or it could be a disconnected rear tank.

as for the gauge not working, it could be a bad gauge, bad sending units in the tanks, or again, bad selector valve.
try disconnecting the sending unit wire off one of the tanks with the switch on the selected tank. if the gauge moves, you know it is in the senders. if it don't you will have to dig deeper.
if i remember correctly, grounding the wire will give you full tank reading,
take the wire off will give you empty tank reading.