Trailer connectors in North America

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.

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.

These converters usually don't handle the case of separate position light circuits for left and right side in the towing vehicle.

SAE J560 was introduced in 1951, which means that older heavy duty vehicles (vintage) may have other connectors.

This is common for RVs and other large trailers which have additional loads beyond the basic for tail lights and brake/turn signals.

This contact occurs on medium duty trailers that have both reverse lights and electric brakes.

A distinctive feature of the trailers that require this type of connector is the fact that they do not have their own braking system and stop along with the towing vehicle.

[11] Introduced by John Deere for agricultural hardware,[12] then used for other purposes, like yachts and general electric cables.