Hummer H3. Manual — part 1450

The front and rear position lamps are turned ON when the headlamp switch is placed in the
position lamps position. The underhood fuse block supplies battery positive voltage to the
position lamp relay switch contacts and the position lamp relay coil circuit. The body control
module (BCM) provides a ground control circuit to the position lamp relay coil circuit. When the
position lamps are requested ON, the BCM energizes the position lamp relay and the park lamp
relay. Current flow is from the relays to the front and rear position lamps. The front position
lamps are grounded at G105 and the rear position lamps are grounded at G420. If the headlamps
are activated by either the headlamp switch or the BCM in Automatic Lamp Control (ALC)
mode, just the front position lamps will be disabled. The rear position lamps remain illuminated
and now act as the tail lamps.

Turn Signal Lamps

The FRT/TRN/HAZ/CRTSY/MIRR and REAR/TRN/HAZ fuses in the underhood fuse block
supplies battery positive voltage to the body control module (BCM). When the turn signal switch
is placed in either the left or right position, a signal is sent to the BCM to illuminate the desired
turn signal lamps. The BCM has an internal flasher that sends an ON-OFF voltage signal to either
the left or right turn signals and their instrument panel cluster (IPC) indicator. When the hazard
switch is pressed, a separate ground signal is sent to the BCM to activate and flash all turn signal
lamps including both IPC turn indicators. The front and rear turn signals are grounded at G105,
G350 and G340.

The IPC illuminates the TURN SIGNAL ON indicator in the driver information center (DIC)
when the IPC determines that the turn signal is active for more than 1.2 km (0.75 mi). The BCM
sends a class 2 message to the radio in order to activate the audible warning.

Stop Lamps

The STOP fuse in the underhood fuse block supplies battery positive voltage to the normally
open stop lamp switch. When the driver presses the brake pedal, the switch contacts close and
battery positive voltage is supplied to the body control module (BCM), electronic brake control
module (EBCM), powertrain control module (PCM) and the center high mounted stop lamp
(CHMSL) which is grounded at G350. The EBCM may also supply battery positive voltage to
activate the stop lamps during specific ABS events.

Backup Lamps

The BCK/UP LPS fuse in the underhood fuse block supplies battery positive voltage to the
normally open park/neutral position (PNP) switch of a vehicle equipped with an automatic
transmission or the backup lamp switch if equipped with a manual transmission. When the driver
places the gear selector lever is in the REVERSE position, the switch closes and the current flow
is from the switch to the backup lamps. The backup lamps are grounded at G350 and G340.

2007 Hummer H3

2007 ACCESSORIES & EQUIPMENT Lighting - H3

Off-Road Lamps

The off-road lamps are available in several configurations with lights mounted on the roof and on
the front brush guard. The lamps are controlled by a single, rocker type switch, located on the
instrument panel. When the switch is closed, voltage is supplied to the relays on the off-road
lamps relay control circuit. When the relays are energized, voltage is supplied to the off-road
lamps.

INTERIOR LIGHTING SYSTEMS DESCRIPTION AND OPERATION

Interior Lamps

The interior lighting consists of the following 2 groups. This first group includes lamps that
illuminate the interior and may not be dimmed.

The dome lamp

The footwell lamps

The reading lamps

The vanity mirror lamps

Courtesy Lamps

The courtesy lamps include the reading lamps, footwell lamps and dome lamps. The cargo lamp,
footwell lamps and dome lamp may be manually turned ON or OFF by placing the interior lamp
switch in the ON or OFF position. When the driver places the dome lamp defeat switch in the
OFF position, these courtesy lamps will be disabled. If a door is opened, the courtesy lamps will
illuminate. After all the doors have been closed, the courtesy lamps will remain illuminated
approximately 15 seconds after the last door closes. The courtesy lamps will also turn ON prior
to any door being opened and will remain illuminated approximately 40 seconds when the driver
removes the ignition key. The body control module (BCM) will immediately turn OFF the
courtesy lamps if a door lock command is received with all of the doors closed or if the ignition
switch is turned to either the ON or RUN position. Individual power and ground circuits to each
lamp are supplied by the BCM except for the reading and vanity mirror lamps which are
grounded at G106.

The reading and vanity mirror lamps can be activated individually by the switches integrated
within the dome/reading lamp and vanity mirror. Voltage is supplied by the BCM through the
dome lamp circuit with the lamps being grounded at G106.

Keyless Entry Interior Illumination

When the driver uses the door key in order to unlock the doors, the body control module (BCM)

2007 Hummer H3

2007 ACCESSORIES & EQUIPMENT Lighting - H3

receives a door unlock signal. The BCM must have inputs that indicate that the ignition switch is
OFF, the courtesy lamp switch is OFF and all the doors are closed. The BCM will then illuminate
the interior lamps. The courtesy lamps will remain illuminated for approximately 15 seconds after
the door is closed. If the door locks are activated to the LOCK position or if the ignition switch is
turned to either the RUN or CRANK position, the courtesy lamps will turn OFF immediately.

When the driver uses the remote function actuator transmitter to unlock the doors or presses the
panic button, the BCM will keep the courtesy lamps ON for approximately 15 seconds. If the
door locks are activated to the UNLOCK or LOCK position or if the ignition switch is turned to
either the RUN or CRANK position, the courtesy lamps will turn OFF immediately. The BCM
will also keep the courtesy lamps ON for approximately 40 seconds after an alarm event is
completed.

Battery Rundown Protection/Inadvertent Power

The body control module (BCM) inadvertent power courtesy lamps supply voltage circuit
provides battery positive voltage to all of the interior courtesy lamps. In the event that any of
these lamps were to remain illuminated for a period of more than 20 minutes with the ignition
switch in the OFF position, the BCM will deactivate the inadvertent power courtesy lamps supply
voltage circuit to prevent a total battery discharge condition. Only when the ignition switch is
cycled back to the RUN position will the BCM reset the internal timer and reactivate the
inadvertent power courtesy lamps supply voltage circuit.

The BCM also utilizes the inadvertent power courtesy lamps supply voltage circuit as a courtesy
lamp request signal circuit when none of the lamps in the circuit are illuminated. When a reading
lamp switch is activated, the BCM receives the request for lamp illumination and switches to
supplying voltage to the inadvertent power courtesy lamps supply voltage circuit.

Interior Switch and Control Illumination

The second group includes lamps which illuminate the interior switches, controls and displays
that may or may not be dimmed. This group may use a combination of LED, incandescent lamps
and vacuum fluorescent (VF) displays.

The door lock and window switches are supplied voltage through the FRT PRK LAMPS fuse and
cannot be dimmed. These lamps will be illuminated at full intensity whenever the park lamps are
ON.

This second list of components are supplied voltage through the body control module (BCM) and
can be dimmed.

Hazard switch

2007 Hummer H3

2007 ACCESSORIES & EQUIPMENT Lighting - H3

Headlamp and panel dimmer switch

HVAC control head assembly

Instrument panel cluster (IPC) via class 2 signal

Radio

Rear window wiper/washer switch

Accessory switch

Sunroof switch

When the ignition switch is turned to the RUN position, the radio VF displays turn ON at
maximum brightness. When the park lamps are ON, all dimmable incandescent back lighting
illuminate at the dimming level indicated by the I/P dimmer switch and all the other back lighting
lamps illuminate at full intensity. At the same time all VF displays dim to match the indicated
dimming level. The panel dimmer switch potentiometer is an input to the BCM. When the driver
selects a dimming setting by moving the I/P dimming switch potentiometer, all dimmable
incandescent back lighting lamps are provided with a specific voltage. When the I/P dimmer
switch is moved from MIN to MAX, all VF displays, as well as all dimmable incandescent back
lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer
switch The grounding for all of the incandescent back lighting lamps is provided by G105 and
G106.

2007 Hummer H3

2007 ACCESSORIES & EQUIPMENT Lighting - H3