Get a wiring diagram - there must be plenty on the internet. Wire socket according to it and fit it to the vehicle - then run the 7 core cable up to the back of the off side light unit and take the internal cover off.
If the vehicle is wired as original you'll find all the relevant connectors there. You'll need to fasten bullets to trailer wires and then use double sockets to connect them to the vehicle system.
I have a relatively expensive crimper which crimps the necks of the bullets with an octagonal impression. Even using the correct bullets I've found they tend to pull off - so now solder them.
Scotchlocks, twisted wires and insulating tape, 2 wires twisted and crimped into one end of a butt splice etc all work - as I've replaced them on systems that apparently worked once.