2004 tahoe trailer brake controller

I purchased a wiring harness from an Ebay site for my Tahoe using a teknsha brake controller. I am trying to determine the correct wiring. The wiring harness has Red (positive) Lt Blue (stop light), Black (ground) and Dark Blue (to trailer brakes ).
I can not get any signal or voltage from the stop light (light blue) wire. Is this normal. Does not matter if ignition is on/off. Have positive and negative working as they should. Anyone know the answer? Thanks in advance

If you do a search for trailer wiring harness you will find some diagrams. On my 2000 silverado I had two use two empty places for fuses in the main circuit breaker panel and a ground from the engine ground on the fire wall. They were installed for this even have a lug to connect to and you just install a fuse. You will need a pigtail for the brake controller which plugs into a plug in the firewall close to the brake. You will find some wires in a harness close to the back of the hitch for the rest of the wires for the seven wire connector. Champion has some wiring diagrams.