The wiring harness runs along the floor for the rear of the truck. It goes threw the floor right under the drivers seat. You should be able to pull back the carpet enough to expose the harness.

 

cool beans, so I dont have to test, do you know the colors?

 

No, sorry.

They should be the same colors at the tails. You may need to find a ground.

 

There should be a LG for the third brake light, that should work for you. The BK/PK should work as well, thats the wire for the park/stop/turn lamp in the rear. Theres a connector on the vehicle underbody, near, LH rocker panel that you can grab the BK/PK at.