Dodge Ram Truck 1500-2500-3500. Manual — part 440

LAMP - CAB & CHASSIS

1. Feed the pigtail wire and connector (2) of the rear

lamp unit (4) through the lamp mounting bracket
and position the lamp studs (3) through the mount-
ing holes in the bracket.

2. For the left side lamp only, position the license

plate mounting bracket (6) onto the rear lamp unit
studs.

3. Install and tighten the two nuts (1) that secure the

rear lamp unit housing to the mounting bracket.
Tighten the nuts to 5 N·m (47 in. lbs.).

4. Reconnect the rear lamp unit pigtail wire connector

to the chassis wire harness connector for the rear
lamp.

5. Engage the rear lamp connector retainer into the

rear frame rail.

6. Reconnect the negative battery cable.

TRAILER TOW CONNECTOR

REMOVAL

1. Disconnect and isolate the battery negative cable.

2. Reach behind the center of the rear bumper to

access and disconnect the connector (2) of the
body wire harness from the 7-way trailer tow con-
nector (1).

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3. Remove the four screws (3) that secure the 7-way

trailer tow connector (2) to the tapping plate (4)
behind the rear bumper.

4. Remove the 7-way trailer tow connector from the

face of the rear bumper and the tapping plate from
behind the rear bumper.

INSTALLATION

1. Position the 7-way trailer tow connector (2) into the

mounting hole on the face of the rear bumper (1).

2. Position the tapping plate (4) over the 7-way trailer

tow connector on the back of the rear bumper.

3. Install and tighten the four screws (3) that secure

the 7-way trailer tow connector to the tapping plate.
Tighten the screws to 2 N·m (17 in. lbs.).

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4. Reach behind the center of the rear bumper to

access and reconnect the connector (2) of the
body wire harness to the 7-way trailer tow connec-
tor (1).

5. Reconnect the battery negative cable.

RELAY-TRAILER TOW

DESCRIPTION

All vehicles are equipped with two trailer tow relays,
one for the trailer right turn and brake lamps and the
other for the trailer left turn and brake lamps. The
trailer tow relays are conventional International Stan-
dards Organization (ISO) micro relays. Relays con-
forming to the ISO specifications have common
physical dimensions, current capacities, terminal pat-
terns, and terminal functions. Each relay is contained
within a small, rectangular, molded plastic housing and
is connected to all of the required inputs and outputs
through five integral male spade-type terminals that
extend from the relay base plate.

The trailer tow relays are located in the Power Distri-
bution Center (PDC) in the engine compartment near
the battery. Refer to the layout label on the underside
of the PDC cover for specific relay cavity assignment
information. A trailer tow relay cannot be adjusted or
repaired and, if faulty or damaged, the unit must be replaced.

OPERATION

The trailer tow relays are electromechanical switches that use a low current input from the Front Control Module
(FCM) (also referred to as the Integrated Power Module/IPM) to control a high current output to trailer brake and
turn signal lamps. Within each relay are an electromagnetic coil, a movable contact and two fixed contact points. A
resistor is connected in parallel with the coil, and helps to dissipate voltage spikes and electromagnetic interference
that can be generated as the field of the relay coil collapses.

The movable common supply contact point is held against the fixed normally closed contact point by spring pres-
sure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This field draws
the movable contact away from the normally closed contact, and holds it against the normally open contact. When
the relay coil is de-energized, spring pressure returns the movable contact back against the normally closed contact.

The inputs and outputs of the trailer tow relays include:

•

Common Supply Terminal (30) - The common feed terminal is connected to a fused B(+) circuit at all times.

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•

Coil Ground Terminal (85) - The coil ground terminal is connected to a fused B(+) circuit at all times.

•

Coil Battery Terminal (86) - The coil battery terminal is connected to a control output of the FCM through a
right or left trailer tow turn relay control circuit. The FCM controls trailer brake and turn lamp operation by
controlling a ground path through this circuit.

•

Normally Open Terminal (87) - The normally open terminal is connected to the trailer lamps through a right
or left trailer tow turn relay output circuit and provides battery voltage to the right or left trailer brake and turn
lamps whenever the relay is energized.

•

Normally Closed Terminal (87A) - The normally closed terminal is not connected to any circuit in this appli-
cation, but will have battery voltage present whenever the relay is de-energized.

The trailer tow relays can be diagnosed using conventional diagnostic tools and methods. Refer to the appropriate
wiring information.

WIRING-TRAILER TOW

DESCRIPTION

The rear body wire harness on the rear frame (1) of
all vehicles is equipped with a take out with a stan-
dard, light-duty 4-pin trailer tow connector (2) that is
secured to the top of the trailer hitch platform (4)
behind the rear bumper. Vehicles equipped with an
optional factory-installed trailer towing package have a
second take out with a connector (3) that plugs into a
receptacle in the back of a heavy duty, sealed, 7-pin
trailer tow connector that is located near the center of
the rear bumper.

Vehicles equipped with the trailer tow package also
include an electric trailer brake wiring provision that
terminates at a connector located on top of the large
body harness connection under the instrument panel
to the left of the brake pedal, as well as an electric
trailer brake pigtail harness and an instruction card (1)
that are stored in the glove box (2) when the vehicle is
shipped from the factory.

Refer to the appropriate wiring information. The wiring
information includes wiring diagrams, proper wire and
connector repair procedures, further details on wire
harness routing and retention, as well as pin-out and
location views for the various wire harness connec-
tors, splices and grounds.

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