New to 2 ton

[74CustomK20]

Hello all, this is my first big truck, and am having some issues I haven't had on my k20's. Brakes are inop, wiring is worse than anything I've ever seen, the rear is stuck in low range, and the dump bed is leaking like a siv.

The bed works, so I can keep adding oil as needed and figure it out.

Is there anything special I need to know about these brakes? It's hydraulic, has a master cylinder...

The wiring is totally different than my k20. The k20 has a square block that the wires all pass through where the cab wiring meets the chassis and engine wiring, which I guess I'm used to. This c70 has a wide buss bar almost and it's a CLUSTER to say the least. My main question I guess is can I take a wiring harness from a half ton or equivalent truck and make that work on this 2 ton? If so that would be sooo much easier. If not, what or where can I find a wiring schematic? Is there anything specifically different between them?

Anything I need to know about these big heavy behemoths lol?