I’ve been trying to figure this out for a couple days now. I’m having troubles with truck running when pcm is plugged in. If I unplug C1 It will start.  If I unplug C3 it will start but say I have C1 plugged in and plug C3 in kills it immediately. Same if it’s other way around. Could this be due to security? 
 

Please help 

I unplugged this wiring harness and left all plugs to pcm plugged in and it fires right up. Don’t have rpm, temp, oil psi now but volts, fuel, and Speedo work and drives fine.

Codes?

None

How are you checking for codes?

Obd2 reader if I plug everything in it will read codes because I unplugged everything but you reset them and it still won’t start and no they don’t come back. Did key trick first thing before messing with it and it said p done. 

The smaller wiring harness there on drivers side fire wall must go to something that is the culprit. 

This is a long shot but I have heard here in the past of whacked oil pressure sensors causing trouble in other sensors. Might try just unplugging it and see what happens. Just spit balling here since I dont remeber the issues folks were going thru. I do remember they had no codes for it either.

Somewhere on this forum in the last couple of years, I remember seeing the identical issue in a post. I don't remember seeing the solution but keep searching and you should be able to find it.