today i found a Plug on
LH side, below the Bed, before the Bumper.
Near to the Left taillight Harness.

The Plug is covered with a Rubber Plug.
i remember 3 females (green yellow brown) wires
and one i think its a male with Big White Wire, because the center hole is much smaller and it looks different

what is this Plug good for

(Green, Yellow, Brown, White) (white is bigger)

 

I think your talking abot the hook up for trailer lights. That works the same as the brake lights you will only have power when you press the brake or have the lights on

 

Okaaaaaayyyy
But i have a Trailer Connector extra for this reason.
with many many pins (Brake, turn, back, fog-back -lights)

 

The 4pin is for simple lights and the 7pin is for more complex lighting