Horn Switch: Description and Operation

Fig.6 Horn Switch:

A single pole, single throw, center-blow, normally open, resistive membrane-type horn switch is secured with heat stakes to the back side of the driver airbag trim cover. When installed, the horn switch is concealed behind the trim cover near the center of the steering wheel. An International Control and Display Symbol for horn is molded into the face of the trim cover to identify the horn switch location to the vehicle operator. The driver airbag trim cover has a regular grid of small nubs molded into the inner surface of the cover directly over the horn switch. When the driver airbag trim cover is installed on the airbag housing, the horn switch is sandwiched between the trim cover and the airbag.

Fig.7 Driver Airbag Trim Cover Removal/Install:

The horn switch consists of two thin, flexible, clear plastic membranes. The center fields of the facing surfaces of these two membranes each has a switch contact laminated to it. The switch contacts are constructed of a thin, electrically conductive copper film. A grid of small, resilient, non-conductive dots applied at regular intervals within the field of one of the switch contacts and a thin bead of the same material is applied around the perimeter of the contact. This non-conductive material suspends and insulates one contact from the other contact, effectively holding the switch open after the edges of the two membranes have been bonded together. Each of two small tabs that extend from the upper edge of the horn switch membranes have a short pigtail wire riveted to it. These pigtail wires connect the two horn switch contact membranes to the vehicle electrical system. The black pigtail wire on the left tab has an eyelet terminal connector on its loose end, while the loose end of the red pigtail wire on the right side has a male spade terminal connector.

The horn switch is only serviced as a part of the driver airbag trim cover. Refer to Driver Airbag for the proper driver airbag trim cover service procedures. The horn switch cannot be adjusted or repaired. If the horn switch is damaged or faulty, the driver airbag trim cover and the horn switch must be replaced as a unit.

The horn switch allows the vehicle operator to manually control the operation of the horn system. When the center area of the driver airbag trim cover is depressed, the nubs on the inside of the cover contact and compress the horn switch membranes. Compression of the horn switch membranes forces the two electrically conductive contact surfaces within the horn switch against each other and closes the horn switch circuit. When the driver airbag trim cover is released, the combined resistive tension created by the non-conductive resilient dots and bead on the one switch contact restore the separation between the two electrically conductive contact surfaces and open the switch circuit.

The only input to the horn switch is a ground feed that is connected to one of the switch contacts through the black pigtail wire. The eyelet terminal connector of the black pigtail wire is secured under a hex nut and washer to the upper left stud of the airbag inflator on the back of the airbag housing and is grounded through this connection when the airbag housing is installed on the steering wheel. The only output from the closed horn switch contacts is the ground path it provides to the horn relay through the red pigtail wire of the horn switch on the horn relay control circuit. The male spade terminal of the red pigtail wire is connected to a mating connector on a take out of the steering wheel wire harness.