MP 875 Modem User Guide
Note: If you choose to install a
separate switch, it must be
connected to the white ignition
sense wire, not the red battery
wire, so that the MP modem can
perform a controlled shutdown,
as described on page 27.
• When the ignition sense line is pulled low (less than 2 V),
the MP modem performs a controlled shutdown sequence
(under software control), de-registering and saving any
relevant operational data before powering off.
Ignition sense options
There are three ways to connect the ignition sense wiring:
• Engine on only. Connect the white ignition sense wire to
the vehicle’s ignition switch so that the MP modem is
powered on only when the ignition key is switched to the
full “On” position, that is, when the engine has been
started. In this configuration, the engine must be running for
the MP modem to be on.
—or—
• Accessory on. Connect the white ignition sense wire to the
vehicle’s ignition switch so that the MP modem is
powered on when the ignition is switched to “Accessory”
mode. In this configuration, the MP modem is on whenever
other vehicle electrical devices can be switched on—such as
when the radio and windshield fan can run.
—or—
• Separately switched. Connect the white ignition sense
wire to a separate switch mounted in a convenient
location, which allows the MP modem to be turned on or
off regardless of the position of the ignition key. In this
configuration, the MP modem can be powered on or off
even if the key is not in the ignition.
The MP modem also has a “Power Off Timer”. When power is
removed from the ignition sense wire, the MP modem remains
on for the period defined by the Power Off Timer, up to a
maximum of 240 minutes. The Power Off Timer is configured
in 3G Watcher. See the online help in 3G Watcher for details.
Ground the power harness
You must connect the black ground wire from the power
harness to the grounded negative terminal of the vehicle
battery, or another appropriate electrical ground. Failing to
ground the power harness properly may damage the MP
modem, may cause radio interference, and can be dangerous.
(See “Ground the MP modem” on page 24.)
The ground wire in the MP modem power harness is not
fused.
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