GMC Sierra Hitch Wiring - 1999 - 2018 - autoanything Reviewed By Dave M (ARVADA, CO) Reviewed for a 2016 GMC Sierra —1/17/2018 8:13 PM. I really like this Curt wire harness. It is so easy to install into the existing wiring. No splicing required. Just pull out the wire fitting from the 7 way trailer plug and then plug in the new one.4.7/5(65) gmc trailer wiring harness | eBay www›Search›gmc trailer wiring harnessFind great deals on eBay for gmc trailer wiring harness. Shop with confidence.