Brake Controller Wiring Question

Hi all. I have an 05 Tacoma V6 with the towing package and have bought a Tekn osha XP Voyager controller. I have wired up a few of these in the past but not with a harness to connect to like we have.

My question is regarding the small gauge brown ground wire that is part of the pigtail that came in the glove box. Do I hook up the white 14 ga. ground wire coming out of my controller to the little 18 ga. brown ground wire on the pigtail? Hooking a 14 ga. wire to a 18 ga. wire on a primary power circuit just goes against my grain, so I could use a little clarification. I did read the towing bible but just want to make sure. Thanks in advance for any help on this.

 

Well I wired it up last night and did connect the ground wire from the controller to the brown wire on the pigtail. The controller instructions say to run the controller ground (white) wire to battery ground directly and that is what I have done in the past.
I can only assume that the small brown wire on the pigtail is a relay conrtol side ground and thus the small gauge wire. Gonna hook it up to the trailer tonight and set the controller power and sensitivity. Just wondering if I should splice the controller and pigtail ground together and then run them to the battery ground??????

 

Just as a follow up, I towed a 3700 lb. fully loaded pop up trailer 300 mi with no issues. I had the back of the truck also full of gear, fishing poles, ice coolers, wood etc. The rear suspension sagged, but was about an inch and a half above the stops. Need a weight distributing hitch next time!