E30 Wiring Harness (Standalone Questions)

[BadDays]

Hey! I'm calling for the folks who have previously made a standalone wiring harness for their E30's or who know a ton about them.

I need to ask if you have reused the C101 plug that connects into the body harness of the E30 along with the diagnostic plug from the original harness for your standalone application?

(This goes for all E30's including the 84-85 318i, Early Models with the square c101 and the round c101 plug for late models.)

[Panici]

Is C101 the connector right at the fusebox? Top right in this photo?

If so, yes I did use it to integrate with the chassis.
I first got the engine running on the floor on the standalone (without the body at all), and then later integrated into the chassis.

[BadDays]

Yes that's the square connector at the driver's top right next to the fusebox, I can make this thing myself but I do need to know how to integrate it into my standalone harness.