Is it ever just "plug and play"?

You can generally buy a what-ever-you-have-on-your-car to a what-ever-
you-have-on-your -trailer adapter at trailer stores. At least from
the car to a four-flat system.

A few suggestions if you rewire.

1) Go to a 4-flat system as that seems to be the most (least?) common
denominator, at least here in the US.
2) Go to LED lighting as they don't have nearly the corrosion issues
that incadescent lighting does.
3) Slather Dow Corning #4 dielectric grease on external connectors and
light bulb sockets to prevent corrosion and keep out water.
4) Use crimp connections instead of wire nuts or solder.

My $0.02.

Good luck, John