That's the bulkhead disconnect, the main pass-through from the engine bay to the interior and vise-versa. It's clearly laid out in the factory service manual wiring diagrams describing color codes and each cavitiy's corresponding position in the harness that plugs into it. It's also shown in post #12.
If you still haven't bought a service manual, you're spitting windward.
The service manual is enroute, I have started to try and familiarize myself with the mess that is under the hood. I did not put 2 and 2 together with the post in #12 so thank you for pointing that out.
