Wiring harness

[Baron]

I'm doing a engine swap to a 76 c-10 with a 5.3 I have a 2007 motor and tranny with no harness or computer. But i do have the harness and computer from a 2000 year. Well my question is. Will the 2000 harness match the 2007 engine and tranny?

[Captkaos]

This is a loaded question, but let's start here.
99-02's used the Blue/Red PCM connector
03-07's used the Blue/Green PCM connectors

03-up used Drive By Wire, the early models used a cable, so if your 07 has DBW, you need a later PCM/Harness.  IF you are willing to swap to a cable throttle, you can use the early harness/ECM. 
Being a 07 5.3L it would have a 58x reluctor which means the 2000 computer won't be able to control it.
If you swapped everything over you would need to change too much stuff to run the 2000 computer on the 07.