Trailer Reverse & Cargo Lamps for a specific application:
http://www.pirate4x4.com/forum/electrical-wiring/2283114-trailer-wiring-diode.htmlThe center wire in the diagram is the trailer battery charge circuit in a standard 7-terminal trailer connector.
This circuit works with or without the trailer battery, but obviously the lights won't work unless the trailer is connected to SOME battery some way or another.
