Another "What are these wires?" question...

2016 Platinum.
Why is there a bundle of wires under the rear bumper?

 

Does not look factory, Where does the end of it go?

 

That’s a port installed option, its either the bed lights or power tail gate lock. Both are universal parts so the extra wiring is bundled up.

 

All that weight might lessen the MPG..

I bet you're right.
Extra wire for an 8' bed..

 

This.
For bed LEDs.

 

I have bed lights. I don't have a power lock on the tailgate.

 

Crawled under the truck today and verified that this is tied into the bed lights. I guess for a long bed it needs more wire and they use the same harness. There were no extra/empty plugs in that bundle.

 

Found this part of the bed lights install PDF. It mentions the extra harness length.