Help! '55 Cruiser 26 hitch wiring re-do...new to this!

[55CalCruiser]

We are new to Airstreaming, and bought a '55 all original Cruiser.
Hitch wiring insulation was crumbled where it entered the body causing shorts.

Found that instead of running in the frame, the wiring goes between the interior and exterior wall.

I removed the cabinet and fresh water tank, cut an access hole, ran the new wiring plug inside, separated the old wires, reattached according to how I color coded them, and cant get them to work.

What should be neutral (white) doesnt work. When I connect to a green lead, it works.

Is the body of a '55 negatively grounded?

Is there a way to find which wire on the airstream is ground? A process of elimination?

Should I take this to a pro?

I feel I am so close, yet defeated.

Any help?

Thanks!