TERION UM20-100111B, Installation Manual, Page: 38 / 78

7.2 Connection to Power Source
1. Run the power cable from the ITU to the tractor’s fuse box. The power cable is a
three-wire ribbon with the round ITU plug attached to one end. All exposed ribbon
wire must be placed in split tubing. Whenever possible, run all exposed wires under
the flooring or behind the various cab moldings and cover plates.
Red = connect to a continuous
hot circuit
Yellow = connect to a
switched circuit.
Black = connect to a ground
point.
WARNING! PANEL AND COVER SCREWS CAN PENETRATE
WIRES AND CAUSE A SHORT CIRCUIT. WHEN REATTACHING
PANELS AND COVERS, MAKE SURE SCREWS DO NOT TOUCH
WIRES.
2. Identify the ground, switched, and non-switched circuits. Locate the fuse panel and
remove the cover. Use a Volt-Ohm meter (VOM) to verify the switched (with key),
non-switched, and ground points.
a. a. To identify a negative or ground point in a tractor, disconnect the cover to the
truck battery compartment. Switch the VOM to the resistance or ohms position.
Attach a long test lead from the negative VOM input to the negative battery cable.
Using a test lead connected to the positive input of the meter, touch the test lead
to the same point on the battery cable and adjust the meter to read zero (0) ohms.
Adjust (zeroing) the meter this way compensates for the resistance present in the
test leads, themselves, so that subsequent measurements will be more accurate.
Now, use the test lead connected to the positive meter input to measure the
resistance to measure resistance at various points until you find one with very low
resistance.
The resistance must be less than 1.0 ohm. This point will be used to
connect the black wire.
Note: Some meters, particularly digital ones, cannot be
manually adjusted to zero. If the meter cannot be zeroed, make
a note of the resistance reading with just the two test leads
touching and subtract that value from your other readings as
you look for a good ground point.
b. b. Identify a non-switched or primary positive power source. Leave the ground
lead connected. Switch the VOM to the DC Volts position. With the ignition
7-2
Mobile Messaging System Installation Manual June 15, 2001
UM20-100111B Terion, Inc.