New parts are generally NOT as reliable as factory parts. I would (and DO) prefer to have working factory parts of any age than unknown imported aftermarket crap. If you choose to put in a new pump, KEEP the original. You may need it.

Since far more people have '87-up trucks, it's not surprising that you hear more people saying overfull is open circuit, since that's the case for magnetic (balanced) 3-pin gauges. But pre-'87 gauges are thermal (2-pin). This shows a cluster with 4 2-pin gauges on the right side of the cluster (Left in the pic, since the cluster is backward):


(phone app link)

 

Thanks for the info. Now, I am seeing something weird and hopefully you can elaborate. Front tank pump and sending unit is working as normal. Rear tank sending unit rod is tied up so it should read full. For some reason, whether you switch from front or rear tank, the gauge still shows the level of the front tank. Not sure what that is? I thought it could be a total coincidence that the rear SU may be working as it can, and the front tank has that amount of gas in, but running the truck for a while, down to a 1/4 tank, shut off truck, then flip to rear tank and it pegs on 1/4.

 

That's confusing... There is no peg at 1/4. Gauges "peg" at each end of their ranges. And the gauge shouldn't do anything if the key is off.

If the gauge doesn't switch, then the switch wiring might be bypassed so it always shows one tank.

 

Got my new fuel pump installed, regardless of if it fixed the problem, it needed to be replaced due to rust. At any rate, I just was doing some researching and found that my truck is one of the rare ones to have the electrical tank selector. I also read somewhere that the selector itself is what tells the gauge what to show, so if the selector fails, the gauge will show whatever tank it got stuck on regardless of switching the tank selector switch. To your knowledge is that true? I'd like to get a bolt meter to the selector switch but can't quite get my hands back behind the dash.

 

Post pics of the selector valve. If you can't reach the wiring at the dash switch, check them at the selector valve.

http://www.supermotors.net/forums/th...-and-or-videos

 

My selector valve is the 6 barb style with the 5 wire plug. Now that I have some free time and it isn't night (truck is loud) I got the chance to start it up and lo and behold gauge and pumps flip back and forth, but only when the truck is running... I will still ****** a fuel selector switch and selector valve next time I am at the JY. I'll see if that might fix it, and if not, then I'll have spares.