Cargo trailer battery?

[candjmc]

We bought 2006 continental cargo 7x16 enclosed trailer. I am trying to figure out interior light, looks like red,blue,black, and i believe white coming out of the wiring harness going uo into the trailer,but when I pulled off wall switch there was a yellow one there. .?

[4x4van]

For any trailer, you'll of course have running lights, right turn/brake, left turn/brake, and ground. If your trailer has brakes (my 16x7 enclosed trailer does), then you'll also have a wire for that. The standard trailer wiring colors are:

Brown=Running
Green=Right turn/brake
Yellow=Left turn/brake
White=ground
Blue=electric brakes
Red=battery/aux (this would typically be used for interior lighting)
Purple=back-up lights

Use a continuity tester and see which terminal (on the trailer plug) corresponds with each wire in your "box". Standard trailer plug layout diagrams can be found at etrailer.com