[GATC35]

Do you have a "chip" installed?

If so take it out and see what happens. I have a buddy with a 99 F-250 that did werid things with a chip installed. When he connected a trailer and disengaged overdrive all kinds of crazy things happened. We spent hours in wiring manuals trying to figure it out. All problems solved when chip removed.

The overdrive button on end of gear selector is a known problem area for shorting out.

Also try going to " the dieselstop" web site lots of good folks there.

Gather this info before searching the "dieselstop".

does door dinger sound with door open and key in ignition?
turning ignition to on , not trying to start, do instr lights test?
turning ignition to on. not trying to start, does "wait to start" light come on?