Body armor rear bumper towing harness

I got a rear bumper for my truck and i love it. Its not a high clearance bumper and it was pretty much unbolt the old bumper and bolt the new one. The only problem that i have it the towing plug. The wire harness is like 4 inches too short i want to cut the tow harness and extend it about 5-7 inches. What gauge wire should i use. Btw my truck is a 2019 dcsb sr 4x4 auto if that means anything

 

Etrailer makes an extension, it's not the cheapest, but you also get a 4pin to play with.

 

i opted for doing it myself because i wanted to do it as soon as possible