MILEPOSTS Garage - The Online Classic Car Magazine 1971 Ford Thunderbird Two Door Hardtop front bench seatCould disaster be lurking here? This seat may look comfortable enough right now, but could there be danger hiding in the padding below?
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Vol. 2, No. 10
January 9, 2004

Automatic Seat Back Release Fire Danger
by The Automotive Mileposts Staff

Image: MILEPOSTS Garage

OK, heads up everyone with a 1970-1979 Ford Thunderbird Two Door, Continental Mark III, Lincoln Continental Coupe, or possibly many other cars equipped with automatic seat back release solenoids!

We've had several people contact us over the past few months advising of problems with these devices. It would seem in some models they aren't protected by a fuse of any kind, so if they short out, or ground out due to a frayed wire, they can heat up and set the car seat on fire! So far, the culprits involved have been a 1970 Ford Thunderbird, a 1975 Continental Mark IV, a 1978 Continental Mark V, and a 1974 Lincoln Continental Coupe. Similar solenoids were used on Cadillac Fleetwood Eldorados, Buick Rivieras, and Oldsmobile Toronados of the seventies, although we haven't had anyone tell us they've had problems with them. It's likely many other two door hardtop cars of this period have similar seat back release solenoids, but again, at this time, we have no reports of problems with them. All of the cars involved also had a power seat, although the power seat itself doesn't appear to have any connection to the potential problems with the seat back solenoid.

In one instance we were advised of, the fire department was able to put out the fire before the car was a total loss. It was determined that one of two things happened: either the wires going to the seat back solenoid had slipped out of a retainer clip, and had grounded to the seat frame somehow, perhaps from years of constant friction. This possibly caused a continual flow of power through the solenoid, which got hot and caught the seat material on fire. Or, the wire itself could have caused a spark and ignited the material.

These solenoids normally were either standard equipment on luxury cars, or came grouped with the power door lock option. You hear these solenoids as you open and close the door. They normally make a loud "thunk" noise. This is the sound of the solenoid releasing the latch on the seat back.

When safety regulations required car makers to install seat back locks on cars beginning in 1968, people were no longer able to move the seat back forward without first manually releasing the latch. Some latches were relatively easy to reach, placed on the outboard side of the seat, while others were placed in the middle of the seat back, facing the rear seat, not so easy to get to. Either way, it wasn't convenient to release the latch if your hands were full. Responding to complaints from consumers, car makers began installing electric solenoids in the seat backs of luxury cars sometime around 1970. This eliminated the need to release the latch manually, but still met safety regulations in that the seat back would be locked in place unless a door was open.

Normally, the solenoid is tied into the courtesy light circuit. Sometimes, an additional switch is installed in the door jamb area, just like the courtesy light switch, to engage and disengage the solenoids as the doors are opened and closed. Very convenient. But not so convenient if the car catches fire.

These solenoids can also run a battery down really fast if they get stuck while engaged, which adds something else to your list to check if you notice your battery dying a slow death.

Next time you have a few minutes to spare, remove the trim panels from the seat back and check the condition of the wiring going to the solenoid. The solenoid is normally a cylindrical shaped object. Also check to make sure any movable parts in and around the solenoid are clean and lightly lubricated. Even in an enclosed area like a seat back, dirt and grunge still build up. This can cause the solenoid mechanism to become sticky, which is a prime reason they burn up or short out.

It's important to remember that these cars have long outlived their intended life span. They weren't designed to be around this long. The fact that so many are still around proves the designs were well thought out, and the cars were well built. Now that they've been given the chance to grow old, it's up to the owner to look for signs of old age and make corrections, hopefully before problems develop. Automotive Mileposts recommends that batteries be disconnected if the car isn't going to be used for a while. Fuses and circuit breakers get old too, and it's not worth the risk of leaving the battery connected if the car isn't going to be driven for a couple of weeks.

If you're unsure of the condition of the wiring, or of the solenoids themselves, simply unplug them. There's normally a plug under the seat, one on each side. You can still use the manual latch release to move the seat back forward. That way, you don't have to find out the hard way that the warm seat you felt wasn't a seat heater!

Copyright © 2004, Automotive Mileposts, Inc.
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