The dominant plug for trailer wiring is the flat pin 7-way plug. There are two main standards, RV code and utility code, and then there are three or four variations of these for manufacturers who wanted to be irritatingly different, like Featherlite. Utility code came first, RV code came later.
- Utility code is W-ground, L-brake, R-charge, B-tails, Y-left, G-right, K-reverse.
- RV code is W-ground, L-brake, K-charge wire, Y-reverse, G-tails, R-left, B-right.