As for the sending units, years and years ago, my front tank (steel) sending unit hadn't worked since like almost brand-new and I found a write-up on some site or other, maybe this one, where some guy discovered that the generic J.C.Whitney gauge sending units had the same electronics as that of our trucks; the same ohms resistance or somesuch ununderstandable over-my-head language.
I got myself the J.C.Whitney unit and retrofitted the necessary pieces onto the Ford assembly as per the wonderful pictorial instructive article and it is still working fine to this day.
I spent many hours of trial and error and got the gauge where Full is Full and Empty is maybe half-an-inch left instead of the gauge laying on Full for the first half-a-tank and then dropping like an anvil.
Like most of my repairs, that J.C.Whitney fix has more than far outlasted the original Ford junk.
Some years ago, I provided links to the instructions and links to the J.C.Whitney sending unit and took several cussings from people who probably screwed up the assembly somehow and then blamed me for pointing them in that direction.
All I can say is that mine is dead-on accurate and has been for many years and still going strong.
After saying all that I will say this, the factory two-tank set-up is highly problematic at best and after having several of those junk original fuel selector valves strand me in dangerous busy intersections and on the bypass at Atlanta, for the last many many years, I have two four-position Weatherhead manual fuel selector valves; one changes Draw and the other changes Return; I wouldn't have another electric valve on my truck and five big hunnert-dollar bills taped on it.
I couldn't count how many people I know who have ran around for years running on whichever tank was selected when the electric valve gave up the ghost and the other tank sloshing around with however much fuel was in it when the valve gave up.
My Front and Rear tank gauges are switched by a big DPDT switch that resides in the area between the driver seat and door, right beside my two manual tank selector valves and Mico Lock; the switch is oriented such that it switches fore and aft; Forward being Front tank and Rearward being Rear tank.
The big 52-gallon auxilliary has a separate gauge all of it's own.
Someday, I intend to put the front and rear tanks on individual gauges as well; such that, I can look at the level of any of the three tanks at a glance without having to mess with a switch and wait for the gauge to start reading --- it takes a bit for the gauge to start reading when switched from one to the other.
Back to the manual tank selector valves; besides having three tank positions, there is an OFF position which has came in handy on a number of occasions when I needed to completely stop the flow of fuel without having to stick the nose of a spark plug in a line.
Having the OFF position is probably a good anti-theft device as well --- providing one can remember to switch the fuel back ON and not start down the road and run out in the middle of pulling onto the highway and it take a few valuable minutes before it dawns on them to turn the fuel ON.
Plus, being able to switch the Returns independent of the Draws is a huge bonus; as, if I want a tank Empty for whatever reason, I can send the Return from that tank to another and it is surprising how quick it will pump Empty when the Return is going somewhere else.
