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FORD LIGHT SWITCH ASSEMBLY FIRES

We are familiar with the Ford ignition switch fires and the large recall issued in an effort to correct this problem. Over the past two years, this office has experienced fires caused by another potential problem in Ford vehicles. The problem exists within the dimmer portion of the headlight switch in Ford vehicles.

The light switch involved is a Model SW-2103. These are the pull out type headlight switches usually located in the lower left corner of the front dash of Ford vehicles. The headlight portion of the switch has two pullout positions, the first for parking lights only, and fully out for headlights and parking lights. The shaft of this pull-out light switch can be turned clockwise and counterclockwise which activates a dimmer switch, lowering and raising the intensity of the lighting in the instrument panels respectively. Fully rotating the shaft counterclockwise past a notch activates the interior lights within the vehicles. The potential problem exists within the dimmer portion of this switch.

The dimmer mechanism consists of a metallic resistive coil set inside a ceramic disc positioned over the shaft of the switch. The coil is exposed on its front side away from the passenger compartment. The front side of the coil passes across a contact permitting a current to flow through a certain portion of the coil when the switch is pulled our in its first or second positions. The greater amount of coil through which the current is permitted to pass (clockwise most position) creates the greatest resistance and therefore dims the dash lighting to its lowest intensity. The opposite position provides greatest intensity.

Through our investigations, we have found that the coil can fail owing to wear and/or possible material defects or damage. A fractured coil can maneuver itself free of the ceramic disc permitting it to come in contact with the metal bracket which mounts and grounds the switch to the vehicle. When this occurs, a current can flow through a portion of the coil creating high temperatures melting the metal material of the coil and possibly igniting surrounding combustibles. This mechanism has been observed in three separate incidents by this office. Two of these resulted in a fire.

The mechanism is precipitated by wear and/or defect in the coil mechanism. If the former is true, we expect there will be an increase in fires caused through this mechanism given an increase in service time. To this date the problem appears to be somewhat limited. However, this particular light switch has been utilized in numerous Ford vehicles. Therefore, a small increase in failure rate owing to age and wear could result in a significant increase in fire losses.

The SW-2103 Light Switch Assembly discussed above is reportedly installed in the following Ford vehicles:

FROM

TO

 

1986

1997

Ford F100, Ford F150, Ford F300

1990

1994

Ford Explorers

1987

1994

Ford Tempo and Topaz

1989

 

Ford Thunderbird and Cougar

1987

1988

Ford Lynx and Lynx LN7 (Sport Model)

1987

1994

Ford Ranger Trucks

1987

1990

Ford Bronco II

1992

1997

Ford Aerostar

 

To conclude, if you observe a fire in a Ford automobile originating in the front dash area, it will be necessary to assess whether the above mechanism is involved in the cause of the fire. Even though the Ford ignition switch fires are fairly frequently experienced, this and other possibilities must also be addressed in detail. Do not hesitate to call the Walters office nearest you.

 
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Walters Forensic Engineering | 277 Wellington Street West, Suite 800 | Toronto, ON M5V 3H2
Information contact: engineering@waltersforensic.com