But even though they've been warned and offered a repair, CBS News Correspondent Sharyl Attkisson reports that some of the owners are not doing anything about it.
Laura Voos says her Ford pickup was parked and locked last week when it suddenly burst into flames in her Texas driveway.
"It was already getting the eaves on the garage when I came out," said Voos of the fire.
She managed to save the house but not the truck, which is now a burned mass of metal. More than 400 Ford vehicles have caught fire since 2000 and at least three people have died.
"It could've been much much worse if the truck had been in the garage," Voos said. "I wouldn't have known until the garage was gone."
Ford identified the culprit in some of the fires as the cruise control switch. In February, they began recalling 800,000 pickups, Expeditions and Navigators.
The big question for federal safety investigators is whether millions more Ford vehicles that used similar switches all the way up until 2003 should also be recalled.
Ford wouldn't let CBS News into a dealership. But Mike Bucy, an independent mechanic, showed Attkisson the cruise control switches on a Ford vehicle.
Bucy demonstrated how there could be a fire regardless of whether the car is on. A tester lit up indicating power on a wire — even though the car was off.
That's normal. It's what happens next that's the problem. Federal investigators say flammable brake fluid somehow gets to that live wire in the cruise control switch and ignites.
A Ford test video, turned over as evidence for a lawsuit, shows how a switch can catch fire. But Ford says it's still not sure what's behind the problem with the recalled switches.
Replacing the switch in recalled vehicles is fairly easy. But to complicate matters, federal investigators say the switches might be only part of the problem.
Meantime, less than half of affected owners have had their switch replaced, even though Ford has sent several recall letters, approved by the government.
The former head of federal highway safety, Joan Claybrook, says Ford's recall letters don't sound urgent enough. She used to require much stronger wording.
"It should have in the title and as a headline on the letter itself: safety recall, recall notice, high risk, or danger," Claybrook said.
Ford says that kind of language might scare consumers too much. But the absence of such wording might be why Laura Voos didn't feel the need to rush down and get her truck fixed when she got a recall reminder — just a week before the fire.