I have a 96 F250 automatic 2wd with a 7.5 460. My fuel gauge is not reading on either tank even though I know there is fuel in them. I haven't had this truck long and don't know how long it has been out. The fuel switch works because I can tell when it switches. I also have a tap under the hood on the passenger side. I have read that it could be a lifter which aren't adjustable or a manifold gasket or bolt loose. It's not loud just noticeable. Any advise would be great.

 

It would very rare to have both fuel sending unit go out, more than likely it is the fuel gauge itself.

This diagram from a 1991 model is very similar to your truck.

Use a DVM to measure the fuel sending unit resistance for each tank. If they measure good then you could have a bad switch, which you can also test with a DVM, or the gauge itself is bad. The fuel sending unit resistance should measure between ~22.5 to 145 ohms.

 

You can get a new switch for a couple bucks at a local pick a part/junk yard. If you go and pick it yourself you can take your time in removing the bazel and remember how to do it for your truck. It's easy I did it last weekend. If you want to go this route I can tell you exactly where the pins are and the two screws that hold the bazel in.

Rich

 

Mostly the fuel gauge, as said doubtful both tank units fail together.
As for you tap. 460 are famous for breaking exhaust bolts. Check that. Be careful if you check for loose bolts. I replaced mine with stainless steel bolts & studs & nuts. When they break they usually break off at the head & I have seen where the head has to come off & have a machine shop remove them. Sometimes you can weld a nut on & back them out. Good luck if that is it.
If it is a lifter add a quart of ATF when you change oil. Your right the lifters are not adjustable but a rocker could be loose. Not the norm though. Good Luck

 

Thanks everyone I will check it this weekend when I get some off time.