RAM 2500 Truck 4WD V8-5.7L VIN D (2005)
Rear Defogger Relay: Description and Operation
The rear window defogger (EBL) relay (1) is a International Standards Organization (ISO)-type relay. Relays conforming to the ISO specifications have
common physical dimensions, current capacities, terminal functions and patterns (2). The EBL relay is a electromechanical device that switches battery
current through a fuse in the integrated power module (IPM) to the rear window defogger grid. The EBL relay is energized when the relay coil is
provided a ground path by the control circuitry within the A/C-heater control.
The EBL relay is located in the IPM in the engine compartment.
The ISO-standard rear window defogger (EBL) relay is an electromechanical switch that uses a low current input controlled by the A/C-heater control to
control the high current output to the rear window defogger grid lines. The movable, common feed relay contact is held against the fixed, normally
closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it draws the movable common feed relay contact away from
the fixed, normally closed relay contact and, holds it against the fixed, normally open relay contact. This action allows high current to flow to the rear
window defogger grid lines.
When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, normally closed contact point. The resistor
or diode is connected in parallel with the relay coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the
electromagnetic field of the relay coil collapses.
The EBL relay terminals are connected to the vehicle electrical system through a receptacle in the integrated power module (IPM). The inputs and
outputs of the EBL relay include:
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Terminal (30) receives battery current through a fuse in the IPM only when the EBL relay coil is energized.
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Terminal (85) receives a ground through the EBL relay control circuit only when the A/C-heater control electronically pulls the circuit to ground.
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Terminal (86) receives battery current through a fused ignition switch output circuit only when the ignition switch is in the Run position.
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Terminal (87) provides battery current to the rear window defogger grid lines through the EBL relay only when the EBL relay coil is energized.
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Terminal (87A) is not connected to any circuit in this application.
The EBL 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 ISO-standard relay and for complete rear window defogger (EBL) wiring diagrams.
