Ford Mustang (1999-2004) Service Manual: Principles of Operation

Battery Saver

The battery saver feature provides automatic shut-off of power to demand and courtesy lamp circuitry.

When the generic electronic module (GEM) detects the ignition switch circuits are in the key OFF or removed ignition key positions, power will be disabled after individual time-out periods of 30 minutes for the demand lamps, and 10 minutes for the courtesy lamps. However, the time-out period for the courtesy lamps changes to 30 minutes when the GEM detects that the luggage compartment lid is ajar by means of the luggage compartment lid ajar circuit, or if the dome lamp is switched on by means of the dome lamp circuit. When the GEM detects that the ignition switch is in the RUN, ACC, or START positions, the battery saver feature is disabled.

The battery saver timer for the demand lamps is reset when the GEM detects that the ignition switch is in the OFF or key out positions or when the GEM detects any one of the following conditions:

• the driver or passenger door becomes ajar, as detected by the door ajar circuit
• the luggage compartment lid becomes ajar, as detected by the luggage compartment lid ajar circuit
• the dome lamp switch is activated, as detected by the dome lamp switch circuit

The battery saver timer for the courtesy lamps is reset when the GEM detects that the ignition switch is in the OFF or key out positions or when the GEM detects the driver or passenger door becomes ajar as detected by the door ajar circuit. For vehicles equipped with the remote keyless entry feature, any signal the GEM detects when a valid remote transmitter button is depressed will reset both the demand and courtesy lamp battery saver timers. This battery saver relay then restores power to both the demand and courtesy lamp circuits.

Base Courtesy and Extended Lighting

The base courtesy lighting feature provides interior lighting for the convenience of the vehicle's occupants. The courtesy lamps consist of the map/dome lamps for the coupe and the map lamps for the convertible. All lamps designated as courtesy lamps will be illuminated whenever the GEM detects that the driver or passenger doors become ajar, by means of the driver or passenger door ajar circuits.

The courtesy lamps will also be illuminated when the GEM detects that the dome lamp switch has been activated, by means of the dome lamp switch circuit.

The extended courtesy lighting feature provides temporary extended illumination of the courtesy lamps after the customer has entered the vehicle. The courtesy lamps will remain illuminated for 25 seconds after the GEM detects that the driver and passenger doors are closed, as detected by the door ajar circuits. The extended courtesy lighting feature will be terminated after the 25 second time-out period, or if the GEM detects that the ignition switch has been moved from the OFF position to either the RUN, ACC, or START positions.

Demand Lighting

The GEM does not provide any special features to the demand lighting group with the exception of providing a power source when the battery saver feature is active. The demand lighting group consists of the luggage compartment lamp, the driver and passenger vanity mirror lamps, and the map lamps.

Illuminated Entry with Remote Keyless Entry

The illuminated entry with remote keyless entry feature, provides power to the courtesy lamps when the remote transmitter is used. When the GEM detects that the ignition switch is in the OFF or key out positions, and it detects that a valid remote transmitter unlock button has been depressed, power to the courtesy lamps will be enabled. The courtesy lamp circuit will remain powered until one of the following occurs:

• The GEM detects that the ignition switch has been moved from the OFF, to the RUN, START, or ACC position.
• The GEM detects any valid remote transmitter lock button is depressed.
• The courtesy lamp circuit has been powered for 25 seconds.

If the GEM detects any valid remote transmitter unlock button has been depressed, and the ignition switch is in the OFF or key out position during the 25 second time-out, the courtesy lamp circuits will remain powered for an additional 25 seconds.