DO NOT GROUND THE BROWN WIRE.
It runs your running lights. Ground it and you will blow the fuse - and the lights will stay dark.
Ground the white wire. Just put a ring connector on it and put it under a sheetmetal screw on the body of the tow vehicle.
Yellow and Green are combination brake and turn signal circuits. I think green is left and yellow is right, but I'm not sure.
Blue runs trailer brakes.
Red charges the trailer battery.
This all assumes that you are using the sort of industry standard colors. I've seen all kinds of screwed up trailer wiring - including all one color. Good luck.
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