cap 3rd brake light and interior light wiring

not sure is there a plug i can plug this into or do i have to wire it somewhere?

 

You are going to have to wire it somewhere. There is a company called TAG that makes a little fuse/junction box that is often used in camper shells for wiring these up. Search online and you'll find the parts, or you can wire it up without the special parts but that is on you to figure out.

 

You can tap into the tails brake light wire pretty easily with a T tap and a spade connector so you can unplug it if you ever remove the camper shell. Just look up a labeled wiring diagram to get the 2 colors and check with a multimeter