What is the difference between a 7-pin and 13-pin wiring harness?

The 7-pin wiring harness is generally used for small load-bearing trailers. The reversing lights cannot be connected.
With a 13-pin wiring harness, you can use the reversing lights, permanent current and Charging line to the trailer. This wiring harness is particularly suitable for bike carriers, trailer caravans and horse boxes.