RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Parking Lamp Relay: Description and Operation
PARK LAMP RELAY
The park lamp switch is a direct input to the instrument cluster. The instrument cluster sends a PCI bus request to the FCM to actuate the park lamp
relay.
The park lamp relay is then actuated through the low side control circuit. This circuit is electronically controlled and continuously monitored for
malfunctions.
Fig.11 ISO Micro Relay
The park lamp relay is located in the Power Distribution Center (PDC) of the vehicle. The park lamp relay is a conventional International Standards
Organization (ISO) micro relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns,
and terminal functions.
The park lamp relay cannot be adjusted or repaired and, if faulty or damaged, the unit must be replaced.
The park lamp relay is an electromechanical switch that uses a low current input from the Front Control Module (FCM) to control a high current
output to the park lamps. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the
relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point
away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized,
spring pressure returns the movable contact point back against the fixed normally closed contact point. A resistor is connected in parallel with the
relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the
relay coil collapses.
The park lamp relay terminals are connected to the vehicle electrical system through a connector in the Junction Block (JB). The inputs and outputs of
the headlamp low beam relay include:
-
Common Feed Terminal - The common feed terminal (30) is connected to the park lamps through the park lamp relay output circuit and provides
ground to the park lamps when the relay is de-energized, and battery current to the park lamps whenever the relay is energized.
-
Coil Ground Terminal - The coil ground terminal (85) is connected to a control output of the Front Control Module (FCM) through a park lamp
relay control circuit. The FCM controls park lamp operation by controlling a ground path through this circuit.
-
Coil Battery Terminal - The coil battery terminal (86) receives battery current at all times from a fuse in the PDC through a fused B(+) circuit.
-
Normally Open Terminal - The normally open terminal (87) receives battery current at all times from a fuse in the Power Distribution Center
(PDC) through a fused B(+) circuit.
-
Normally Closed Terminal - The normally closed terminal (87A) is connected to ground at all times.
The park lamp relay can be diagnosed using conventional diagnostic tools and methods.
