this is from the '05, YMMV
FSM 5l-52
Quote:
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.
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.
The signal wire to the BCM goes into the C1 at the BCM pin 19. I don't know what the voltage is to trigger the BCM to turn on the lamp, but I am sure someone around here knows, or give you a place to start
