RAM 2500 Truck 2WD V8-5.7L VIN D (2004)
Heated Glass Element Relay: Description and Operation
The rear window defogger relay is a International Standards Organization (ISO) micro-relay Relays conforming to the ISO specifications have common
physical dimensions, current capacities, terminal patterns, and terminal functions The ISO micro-relay terminal functions are the same as a conventional
ISO relay However, the ISO micro-relay terminal pattern (or footprint) is different, the current capacity is lower, and the physical dimensions are smaller
than those of the conventional ISO relay.
The rear window defogger relay is located in the power distribution center (PDC) in the engine compartment Refer to the PDC label for rear window
defogger relay identification and location.
The black, molded plastic case is the most visible component of the rear window defogger relay Five male spade-type terminals extend from the bottom
of the base to connect the relay to the vehicle electrical system, and the ISO designation for each terminal is molded into the base adjacent to each
terminal The ISO terminal designations are as follows
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30 (Common Feed) - This terminal is connected to the movable contact point of the relay.
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85 (Coil Ground) - This terminal is connected to the ground feed side of the relay control coil.
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86 (Coil Battery) - This terminal is connected to the battery feed side of the relay control coil.
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87 (Normally Open) - This terminal is connected to the normally open fixed contact point of the relay.
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87A (Normally Closed) - This terminal is connected to the normally closed fixed contact point of the relay.
The rear window defogger relay cannot be adjusted or repaired If the relay is damaged or faulty, it must be replaced.
The rear window defogger relay is an electromechanical switch that uses a low current input from the integrated power module (IPM) to control the high
current output to the rear window defogger grid 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 The resistor or diode 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 rear window defogger relay terminals are connected to the vehicle electrical system through a receptacle in the IPM The inputs and outputs of the
rear window defogger relay include:
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The common feed terminal (30) receives a battery current input from fuse 27 (15 amp) in the IPM through a fused B(+) circuit at all times
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The coil ground terminal (87) receives a ground input from the A/C-heater control when the A/Cheater control electronically pulls the control
circuit to ground
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The coil battery terminal (85) receives a battery current input from fuse 36 (10 amp) in the IPM through a fused B(+) circuit only when the
ignition switch is in the Run position
-
The normally open terminal (86) provides a battery current output to the rear window defogger and heated power mirrors (when equipped) through
the relay output circuit only when the rear window defogger relay coil is energized
-
The normally closed terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the rear
window defogger relay coil is de-energized
The rear window defogger relay cannot be repaired and, if faulty or damaged, it must be replaced Refer to the appropriate wiring information for
diagnosis and testing of the micro-relay and for complete rear window defogger system wiring diagrams.
