Whiteman if you go to supacheap and buy a new plug for the trailer(old plug probably stuffed or the screws are rusted), you will find that it has a listing ion the package for numbers wich relate to the colours of wire.
The plug will have numbers moulded near the screw hole to plug the wires in for the corresponding number.
All you will need is a screwdriver and a set of pliers to strip the plastic from the wire.
All the best Kev.