The trailer wiring colors are as follows: red is used for a battery, green is for the right-turn signal, yellow is for the left-turn signal, white is for the ground, brown is for the tail markers, blue is the brake light and purple is for the backup light. The amount of wires on the trailer varies according to what size its wiring clip or plug is.
Not all trailers will have seven wires. The wire clips range among 4-way, 5-way, 6-way and 7-way connectors. The larger connectors will generally offer more features as opposed to trailers that utilize smaller plugs.