Trailer connectors in North America

A number of standards prevail in North America, or parts of it, for trailer connectors, the electrical connectors between vehicles and the trailers they tow that provide a means of control for the trailers.

In the North American market it is very common for brake lights and turn signals to be combined.

On cars and light trucks (listed below as Light Vehicles) there is no formal standard, instead there is a wealth of contacts with more or less accepted standard. However, you can not be entirely sure until you have measured the current connector on the vehicle and trailer that they fit each other.

Heavy Vehicles are standardized through SAE J560 which is similar to ISO 1185.

Note that different color coding can be used for certain functions, which means that you can not trust the colors mentioned here without measuring the contact and wiring from case to case. In some cases - as in the flat 4-pin or 5-pin connector - it is fairly obvious which color that is connected to which pin.

In case you have a vehicle that separates the left and right side position lights into 58L and 58R - like many German cars - it is advisable to choose 58L to feed the taillights. These two circuits shall not be merged because it can create problems in the towing vehicle. If you want to be more advanced you can make a simple connection with two diodes that provide balanced load of the circuits. Note that the diodes have to be able to handle high currents or that they are used to control a relay which in turn feeds the trailer. If you have a trailer with a lot of lights the diode and relay wiring is preferred, but if you have a trailer with a simple light arrangement it is usually sufficient to wire to 58L.

In market there are many special converters that solves the problem of connecting a car with European wiring to a trailer with North American wiring. What most of these converters do is to bring together the turn signals and stop lamp signal from a three-wire solution using 54, L and R into a two-wire solution using L54 and R54 according to DIN where brake light and turn indicator uses the same wire and bulb for each side. These converters usually don't handle the case of separate position light circuits for left and right side in the towing vehicle.

...
Wikipedia