humnbass

I pull a 2 horse bumper pull trailer with my 2006 suburban with the factory tow package using a 7 pin plug. I just installed a new brake controller with the factory wiring harness that plugs in by the driver's side kick panel. The brake controller is not recognizing when the trailer is connected. There is an electric brake signal going to the tow vehicles plug. when I ground a test light to the tow vehicle and place the test light prong on the tab in the plug that carries the signal the brake controller displays as if it's connected to a trailer. When I plug the trailer to the tow vehicle the brake controller does not detect it and only displays a dot on the display. All of the lights work on the trailer as they should. Any assistance would be highly appreciated as I am at my wits end.

thanks.