Truck Wiring harness
 

Hi guys! new to the forum here! HOpefully someone can help me out! I have an 05 silverado and when i plug a trailer into my outlet I do not get running lights. I know it is not the trailer and plug adapter as i bought a new adapter and have tried 4 trailers all 4 do the same thing and those trailers work on other trucks. I put a voltmeter on the 7 wiring harness and the one I do not have power coming up is the brown wire which i belive is the running lights. Any suggestions on how to get this wire to become hot? where does the wiring harness plug into? is it the back lights somewhere? I am leaving on wednesday with our trailer so any help would be greatly appreciated!

Thanks in advance!