It has been a long time since I and a friend wired my 62 C10 truck in to the stock harness. For some reason we ran 1 relay for each PCM connector (1 for red, one for blue).

How much power does the PCM actually require? Will 1 relay for both connectors be suffice?

Very minimal power is required by the computer. My stand-alone harness has one 10A fuse for the battery constant power and another 10A fuse for the ignition power. Relays would be just overkill and are another failure point.

Lets be sure we are on the same page. The PCM does not draw much power. But you also have to power the MAF sensor, 2X O2 sensors, 8X coils and 8X injectors and maybe more if you are attempting to integrate more functions beyond fuel control.

I am building a stand alone harness for just engine control and I am using 1 relay to power the PCM and all the other parts mentioned.

Yeah, I forgot about those circuits. Mine has a fuse for the coils/injectors and another for the MAF/O2 sensors. The only relays being used are for the ignition, starter, fuel pump, A/C compressor and a relay each for the radiator fans.

I guess their determined that their design didn't a main relay for the engine control. I assume you have fuses after the relay for the sensors?