Lamp Bar Switch: Operation
In vehicles manufactured for North American markets, the light bar lamp switch operates on battery voltage received on a fused ignition switch output (run-start) circuit from a fuse in the Junction Block (JB) whenever the ignition switch is in the On or Start positions. In vehicles manufactured for export markets, the switch operates on battery voltage received from the park lamp relay in the JB on a park lamp relay output circuit whenever the park lamp relay is energized. The switch receives a path to ground through a splice block in the instrument panel wire harness secured by a nut to a ground stud on the driver side instrument panel end bracket near the JB.
The switch also receives battery voltage on a fused B(+) circuit that the relay within the switch controls to energize and de-energize the light bar lamps through an output on the lightbar switch output circuit. A panel lamps driver input is used to illuminate the icon on the switch rocker when the exterior lighting is turned On. In certain markets where it is required, the switch also receives a logic input on a low beam driver circuit, which allows the switch to disallow the light bar lamps from operating unless the park lamps are turned On and the low beam headlamps are turned Off.
Another output from the switch is a voltage signal that it provides to the Body Control Module (BCM) on a lightbar switch sense circuit. The BCM sends electronic messages over the Programmable Communications Interface (PCI) data bus to the instrument cluster based upon this input to control illumination of the light bar lamp indicator and/or the high beam indicator as required by the market for which the vehicle was manufactured.
Because of active electronic elements within the light bar lamp switch, it cannot be tested using conventional diagnostic tools or procedures. If a problem is noted with the light bar lamp system operation, test and confirm the input and output circuits of the switch are in good condition before replacing the switch.