Third brake light issues on my ARE topper

Have it wired into the driver side brake light. The thing is, it comes on when I press the brake with the truck off. When I crank the truck and hit the brakes, only the tail lights light up, third brake light does not. Anyone have this issue? I'm an electrician by trade and can read line diagrams, so I'm thinking about running it back to the actual third brake light on the cab. Only thing I can think it could be is there just isn't as much power available to the tail light circuit when everything else is on. Which, doesn't make much sense to me. You would think it would pull the same power as it would on or off. I don't deal with DC much though, so I'm not too sure.

Any ideas?

 

where exactly did you tap the power and ground leads? do you have skid control option on your truck?

 

It's a 2008 SR5 4x4. So the only "options" I have are 2high, 4high and 4low. Nothing fancy. I have the hot from the brake light going to the hot (green with red stripe) behind the base for the lamp and the return going to the solid green behind the same base. It works when the truck is off, what the hell would make it not work with it on?

 

In other words I drilled into my bed and ran the wires for the third brake light behind the driver side tail light and tapped into it from there

 

everything i have looked at on the wiring diagrams have me believing you should be tapping into the blue wire for positive and white/black stripe for ground. i understand the color of wire could be different for the 08'. i think you may have tapped 2 positive wires. one of them is not live until the truck is on but providing a ground until on.

Green wire should be the positive wire for the parking lamp circuit.
Green/Red wire - i couldn't find a suitable wire on the diagrams.

the diagrams were from the 2006 FSM.

 

One month later update. Finally got around to fixing it. Somehow I missed the black/white wire. Tapped hot into the green/red, and black/white for ground. Worked!