trailering brack wires in rear ?

[fourfourto]

I have the front wires for trailer brake.

In the back there are 4 for signal and lights.

Without tapping in to taillight wires and running a positive wire from the front is there any wires or plug to pick up the blue(electric brake), reverse wire and a power wire ?

I dont have the sub but is there a power wire (or plug)behind the drivers side rear plastic.

My brother said on other GM trucks there is a plug to add a harness for those 3 wires.

Is there a harness available for the 3 ?.
I prefer not cut into wires.

What does the dealer do when adding the 7 prong trailer plug ?

[tower]

You don't necessarily need to cut wires. You do need to start opening up panels to find where the wires run!