The scan tool CANNOT "show 13.6V at the fuel pump" because there's no voltage sensor at the fuel pump.Will do. But scanner showing 13.6v at fuel pump now that truck is running.
The voltage reading is from significantly further forward, where the harness ties into the computer.
You MUST measure voltage as close to the fuel pump as practical, and you can't do that with a scan tool.
Yup, you need to do some tracing and examination of the wire harness with a multimeter. Burnt contacts on the fuel pump relay are somewhat common, and I suppose the same for the contacts in the oil-pressure switch. TEST BEFORE REPLACINGI noticed the fuel pump voltage acting flakey when cranking.....drop to 8 volts...showing 10v koeo.