ALT/GAS Indicator
WARNING: This page is about a different car, the 2004 Ford Pickup Heritage. However, it is still accessible from the selected car via links, so may be relevant.
The ALT/GAS switch indicator is integral to the ALT/GAS switch. The indicator is controlled by the AFCM and is illuminated when operating in CNG mode. If an emission-critical diagnostic trouble code (DTC) is recorded, the indicator will flash with a steady ON, then OFF pulse.