I'm installing a 3rd brake light on my '09 Ram 1500 with an ARE cap. Is this the white wire you are referring to? It is under the rear of the truck by the spare tire. If I run the hot to this wire and the ground to the frame it should work right?

Thanks!

 

Yes, that's the idea. There is a ground nut on the frame a little ahead by the axle. You'll need to tap into constant power on the 7way for a dome light if you have one.

 

yes that is the white wire they used on my cap as well.