no start - PCM problem?"

I purchased a '93 C1500 with a '00 4.8L Vortec conversion earlier this year. Put about 5000 miles on it and it died in the driveway last week. Engine cranks but will not start. It had been more hesitant to start over the past couple of months requiring longer cranking and misfiring sometimes...but now it only cranks and will not fire.
No fuel pressure. No 5v sensor signal at any sensor.
I tried to pull codes off ECM - but the scanner can't communicate. So I checked for power and grounds on ECM connectors. There is no IGN power on blue connector pins 19 and 75. Constant BATT 12v and all grounds check out OK.
Spent hours yesterday travel to unravel the harness and find source of the pink wires running to pins 19 and 75. Both wires join and run into main harness over the intake...
I have found good IGN voltage on wiring coming thru firewall on driver side. The driver inside fuse panel also powers up when key is on and the (1) ECM fuse location is powered. The harness is someone's conversion - so there is confusion on what wire is doing what...
I need to get the truck off driveway and into garage to work on it. Will it damage ECM of any other systems if I jumper a IGN switched 12v power to pins 19 and 75 to see if ECM will power all systems?
Would a bad crank sensor or any other sensor create a problem whereby the IGN power wouldn't get to the ECM? I really would like to get to the root cause of my problem with NO IGN 12v power to the ECM - but I need to get a start so I can relocate truck before the weather turns any worse!!
Any ideas or suggestions? This is no local LS conversion shop in my area.

Thanks for any help.

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