Hi. I have a 91 4.9 f150. Apparently the previous owner had an issue with the fuel pump and fixed it by wiring the high voltage line directly into the fuse box. now the fuel pump runs in high pressure mode all the time. do I need to strip all the tape off my wiring harnesses until I find the break or problem or is there a simpler solution? Thanks.

 

I think I would disconnect the new wire and troubleshoot the original wire. the engine needs to be running to find voltage on the hot wire. if it is a single tank hot wire is red, or for front tank in a dual tank system, and the rear tank brown. most of the wiring harness is in a ribbed plastic sheath that is split and can be opened to probe wire at different places. You can also check for voltage at the emergency fuel cutoff switch located behind the passenger side kick panel. If it is dual tank you can probe for voltage on the red wire and brown wire where the big rubber cannon plug goes through the firewall under the steering column. If there is voltage there then there is voltage at the fuel shutoff switch.