A5 2010 2.0 tdi not starting now

[Katch1971]

Driving me potty no tested everything was coming up low fuel pressure
Can a pressure relief test OK but go bad when installed
Tested prv harness plug 8.5v unplugged but when plugged in and tested there's no voltage
LAST week car was intermittent at running but broke down twice and now won't start
Thanks

 

[DXX]

Maybe shorting to ground when installed?