In the UK, male/female quick release connectors ("red line" or emergency), have a female on the truck and male on the trailer, but a "yellow line" or service has a male on the truck and female on the trailer. This avoids coupling errors (causing no brakes) plus the connections will not come apart if pulled by accident. The three electrical lines will fit one way around a primary black, a secondary green, and an ABS lead, all of which are collectively known as "suzies" or "suzie coils".