Speed Control Indicator (F-Super Duty/Excursion)
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 2005 Ford RV Cutaway, 2005 Ford Pickup, 2005 Ford F550 Super Duty, 2005 Ford F450 Super Duty, and 2005 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.
The speed control indicator is controlled by the instrument cluster. The PCM sends a message through the SCP network (Excursion) or CAN (F-Super Duty) to the instrument cluster to illuminate the indicator when the speed control is engaged.