Reworking Wire Harness after Engine Swap

[CJ2A]

1963 GMC with original 305 V6 swapped to an LS1.

All the wiring diagrams I have looked at show the black wire from the firewall plug on the passenger side as a hot wire directly from the starter. This black 18 gauge wire still has the original clip on end fitting. If this were on the starter it would of had an eye for the fitting, right ?

Am I over thinking this ?

Did GMC’s get there wiring harnesses thrown together with Chevy left overs so this color could be totally off and this is a temp gauge wire?

[Pitpig]

I swapped in an LS with an auto wire kit. I’m not looking at it right now, but the starter has purple wire to fuse box and a red wire from alt via a circuit breaker. The wire you show doesn’t look like a starter wire. 18 gauge looks like a sensor