White: Ground Green: Right turn Brown: Running and tail lights Yellow: Left turn Blue: Reverse lights, which most trailers don't have.
NOTE: In heavy duty 7 way wiring connections, Blue is used for brake hot and is 12ga. It is not recommended for the light weight 5 way wire because it is not a big enough gauge to handle brake operation.
The color code for a 4 wire plug is:
White: Ground Green: Right turn Brown: Running and tail lights Yellow Left Turn:
In theory, the same color wires do the same things. However, it's best to test the trailer wiring before connections. Also re-ground the trailer to the white wire and clean your light bulbs and sockets.
There are several threads in our tow wiring section explaining how to test the trailer lighting and different RV wiring codes.