Check the continuity of the plug is correct using the Ohm part of a meter. You can also strip the plug back or use test leads and a 9 volt battery or other electric source for direct testing.
Also go over your vehicle plug with the volt meter to make sure everything is still working correct with it.
If it has missing pins where you need them, just go buy a new 7 pin plug. $10 is much easier than stressing and trying to rig something.
Seeing you have a 2011, we need to connsider the full equation.
What is your vehicle and does the trailer have LED lights?
With some vehicles, LED lights do not have enough resistance to activate the circuit. A quick google search will help trouble shoot your exact vehicle.