I have a 1999 F150 XLT with V8 and a few years ago I had to replace a leaking heater core. I had to do a lot of "chiropractic" work on many parts of the dash and steering wheel to get the heater core out. I had to do this twice because the stinking replacement also sprung a leak. I think this might be why I am now having a few specific issues. The first one only showed up recently and that is my fuel gauge is reading empty with the empty light on. sometimes it comes back when driving but 95% of the time its all the way down pushing hard on empty. I have run the instrument cluster test and can see that the gauge needle will rotate cycle properly but the "fuel" portion of the test always shows me 255 all 3 or 4 times I have run the test. I cant seem to catch it when the needle is not on empty. I have heard that this could be the sending unit or the anti slosh module and I am much more keen on trying to poke the slosh module if that is truly the answer rather than dropping the fuel tank.

the other issue which has somewhat corrected itself but I want to check its adjustment is how it at one time it would only crank 50% of the time. it seems to be good now but I want to investigate the neutral safety switch or the MLPS but I have not seen a guide specific to hunting that sensor down and am looking for guidance on where to locate that thing. also and probably related, my shifter cable assembly broke sometime around the time I did the heater core replacements. A portion of plastic of that assembly was gummy on the surface and its was brittle as heck. The new cable works fine but I wonder if I bumped something out of alignment. the shift needle seems aligned properly though.

but really, the fuel gauge is my biggest problem at the moment as the truck pretty much cranks every time now. I'm just too curious for my own good and want to check that neutral safety switch while I'm in there for the fuel gauge.

things I think I need to investigate:
where is the neutral safety switch and what is the care and feeding of it to make it happy if it is out of alignment?
where could I find the sending unit wires without dropping the fuel tank so I can do resistance tests to know for sure if its the sending unit or the anti slosh module.

Thanks in advance

 

The start issue could be a bad ground. For example, when I experienced a similar issue just twisting the steering wheel to rock the truck was enough to correct the issue temporarily.

-Mark