Hi all and sorry if this post has been done in the past. I have a beautiful 99 F250 SD 4x4 V10. It has run impeccably until last year. I bought it with 106,000 K's and now has 156,000 K's. Use it for my day to day and pulling a 25' 5th wheel. Problem started a couple years ago and have come to the point of not having a running truck. I have replaced the all relays and the one behind the radio, new spark plugs, egr components, cam sensor, fuel pump ( Delphi ), fuel pressure regulator and PCM ( had a code ) I'm sure I'm missing some stuff.
Problem is my voltage readings at the frame plug to fuel pump plug are zany. Everything is good at inertia switch so it's between there 12.5v last reading and the frame plug 156.8v that connects to the pump plug. What ? at the 12v setting on my multimeter. Obviously I must be probing the wrong wires. Neg to black wire and pos to red wire at frame plug. Truck does want to start but flutters at firing and dies. Priming circuit is not building pressure on my pressure gauge at schrader valve 0psi but still is getting some fuel as it tries to start and dies. It's time to let the experts in on this conundrum and steer me in the right direction. I've worked on vehicles since I was 12yrs old but this one is a doozy. So which wires do I probe at the frame plug to address the voltage irregularity. Could it mean a short from the inertia to pump plug. I did do a continuity test from inertia to plug when changing the pump ( dropped the tank ) and seemed fine on both wires. Partially blocked fuel line maybe ? New filter with new pump. When I use an external battery I can prime the line and it does start and runs a few seconds then dies. Thanks in advance to any and all suggestions All testing done with key on, didn't try to start it during voltage test at plug.

 

knowing fords and ground corrosion issues i would start by finding every ground point and clean them, sadly that trucks 25 years old now there's going to be issues that are hard to find and repair that will drive the best of the best dealer techs to throwing up the hands and say uncle,

 

Even if you had a short that didn't pop a fuse, your voltage would still read ~12.5V. It is a 12V system, and I'm having a hard time figuring out how on earth you'd be reading anything higher. Aside from the output of the ignition coils, everything should be 12V. You should be able to check voltage on the Pink and Black wire coming off the inertia switch for voltage. You should read battery voltage for a few seconds after the key is turned on, and then it will drop off to about 6V or something less (I've never actually done it, just repeating what I've read).

Wiring diagram for fuel system. (2001, sorry, uncertain if the colors are exact on 99 or not)
https://www.ford-trucks.com/forums/1...g-diagram.html

 

That was the measurement with the plug unplugged so that may have caused the unusual reading but was the same at the inertia switch on the pink / black wire. Odd but the open circuit may have caused it. Key in on position.

 

Are you sure your multimeter didn't start reading in mV?