Hi Phil

The overlay harness repair I am sure is to get the sensor wire away from the injector wires that are in the loom, had one the other day that had a new rail sensor with a new harness end spliced on the end of the old loom, Still had rail pressure faults & poor driveability put a new harness in as L/R advise in the TSB & fault fixed

As for high pressure testing you should be able to determine the status of the h/p pump by scoping with frank massey test, also can test blind pressure with a sykes or delphi guage.

Hope that helps

Pete