In Australia, all new trailer units registered after 1 January 1988 have required a minimum seven-pin connector that complies with Australian Standard 2513-1982. This allows enough wiring connections to cope with all trailer lighting requirements. Seven-pin plugs can be round or flat. There are also 12-pin connectors for trailers with auxiliaries, rear fog lamps or electric winches. There are still older trailers around with five or six-pin connectors, and you can either buy adaptors for these or rewire the trailer with a seven-pin connector.
Locate the wires coming out of the back of the trailer lights. Measure and cut each new wire so that there is a sufficient length to run from the trailer light to the tow hitch area so they can connect to the tow vehicle via the plug. Connect the new wiring to the trailer lights using terminal barrel connectors and crimpers. Use color-coded wire if possible; otherwise label each wire carefully if you use all one color.
Color code or label as follows:
Yellow - Left-hand turn indicator (connects to pin 1)
Black - Reversing signal (connects to pin 2)
White - Earth return (connects to pin 3)
Green - Right-hand turn indicator (connects to pin 4)
Blue - Service brakes (connects to pin 5)
Red - Stop or brake lamps (connects to pin 6)
Brown - Rear lamps, clearance and side marker lamps (connects to pin 7)
Route the wires along the trailer and to the tow hitch. Locate wires where they will not contact moving parts or be overheated. Insulate wires at joints and support them at intervals of not more than 600 millimeters to protect them from chafing. Run wiring through the trailer frame wherever possible or keep it high and close to the frame for protection.
Strip the ends of the wire and splice them into the seven-pin connector using the color coding. Connect to a towing vehicle and plug the connector into the towing vehicle socket. Have someone operate the vehicles indicator turning lights, brakes and headlights to make sure all trailer lights work before using.
