Electrical question for truck caps

Picking up a cap pretty soon and wanted to get some thoughts about where/how to pull cable for interior lights and third brake light. I was thinking about pulling straight from the battery, but someone mentioned using the seven way at the trailer.
Any thoughts? is there a right/wrong way to do this?

Thanks

 

I ran a wire from the driver side taillight and up to the cab. There's a grommet under the drivers seat that you can go through and then run it to the fuse panel under the dash. I used a multimeter and found a circuit that was hot all the time and used a fuse tap to get power from it. I ground the third brake light and interior light with a bolt inside the taillight area (I sanded to bare metal for a good contact first). I also wired the brake light to the tail light for power, on mine I believe it was a green/red wire found at the back of the middle bulb.

 

When I had mine installed, they pulled from the drivers side taillight.

 

When I talked to the guys at the leer dealer they said the installed into the 7 way. Apparently leer makes a piece for this. Then he informed me that tying into the battery/tail light will void the factory warranty for all electrical on the vehicle. Does anyone know if this is accurate? if so I'm kind of confused as to how using the trailer power would be any different?

 

Mine's a Leer and most around here are and all come from the same local dealer. All that I'm aware of are wired via the taillight.

He uses those clip on splicers....then runs the wiring harness wires into those.

 

For the 2nd gens there is not a hot wire anywhere on the rear of the vehicle, so if they tie into the trailer harness then you need the key on for power.

 

I pulled the brake light from the driver side and I already had run power straight from the battery so that's how I ran the power for the LED interior lights.

 

For a third gen the leer dealer I talked to showed me a kit that piggy backs off the 7 flat round trailer plug. And you still use the plug for a trailer! But another dealer I talked to had not a clue what I was talking about. Not sure if they just didn’t want to mess with it or didn’t know anything!