trailer harness - whats the single wire with a cap on it??

[hoorders]

Quick question...just got my sierra 1500HD and checking it over to get it ready to tow. The trailer harness(back of the truck) has this single wire with a cap on it it just behind the trailer plug......anyone kow what this is??

I attached a pic.

 

Thanks!!

[jhplak325]

If I recall, that is for the 3rd brake light on caps or in bed campers.

[hoorders]

That would be great if it was for a third brake light. I will check it with my tester to see if it its powered by the brake lights....thanks.

[hoorders]

If I recall, that is for the 3rd brake light on caps or in bed campers.

Bingo!.....yup thats what its for.....thanks!