Horn Relay: Description and Operation

Fig.3 Junction Block Location:

The horn relay is located in the Junction Block (JB) on the right cowl side inner panel, below the instrument panel in the passenger compartment (Fig.3). The horn relay is a conventional International Standards Organization (ISO) mini relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The relay is contained within a small, rectangular, molded plastic housing. The relay is connected to all of the required inputs and outputs through the JB connector receptacles by five male spade-type terminals that extend from the bottom of the relay base. The ISO designation for each terminal is molded into the base adjacent to the terminal. The ISO terminal designations are as follows:
- 30 (Common Feed) - This terminal is connected to the movable contact point of the relay.
- 85 (Coil Ground) - This terminal is connected to the ground feed side of the relay control coil.
- 86 (Coil Battery) - This terminal is connected to the battery feed side of the relay control coil.
- 87 (Normally Open) - This terminal is connected to the normally open fixed contact point of the relay.
- 87A (Normally Closed) - This terminal is connected to the normally closed fixed contact point of the relay.

The horn relay cannot be adjusted or repaired. If the relay is damaged or faulty, it must be replaced.

The horn relay-is an electromechanical switch that uses a low current input from the horn switch to control a high current output to the horns. 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 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 horn relay terminals are connected to the vehicle electrical system through a connector receptacle in the Junction Block (JB). The inputs and outputs of the horn relay include:
- The common feed terminal (30) receives a battery current input from a fuse in the JB through a fused B(+) circuit at all times.
- The coil ground terminal (85) receives a ground feed input from the horn switch through the horn relay control circuit whenever the contacts of the horn switch are closed. On models with the optional Remote Keyless Entry (RKE) system, the horn relay control circuit can also be pulled to ground by the RKE module.
- The coil battery terminal (86) receives a battery current input from a fuse in the Power Distribution Center (PDC) through a fused E(+) circuit at all times.
- The normally open terminal (87) provides a battery current output to the horns through the horn relay output circuit only when the horn relay control coil is energized.
- The normally closed terminal (87A) is not connected to any circuit in this application, but battery current should be present at this terminal whenever the horn relay control coil is de-energized.