After my truck has been started the AUX Brake light comes on and a constant tone accompanies the light. This light and tone continue while the truck is running and in operation. The brakes seem to operate fine. There is an ABS light on also. The ABS light doesn't go out. The ABS light is on when you start the truck with no tone. Again, after a few seconds the AUX Brake light comes on with a constant tone. Any suggestions to diagnose the problem.