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Tuesday, Oct 21, 2014
Autos

Bolt of lightning shocks car's headlight relay

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Dear Tom and Ray:

My uncle owns a 2001 Lincoln Town Car. A few days ago we had a real bad storm, and a tree that was about 7 to 10 feet away from the car was hit by lightning. The bolt grazed the tree and hit down on the ground on a root that was only 4 feet from the car. After the lightning hit, we found the headlights on. We were unable to turn the headlights off using the switch. We had to disconnect the battery cables in order to get the headlights off. Could the car have been hit by lightning also? How would we know if the car actually was struck by lightning? — Shannon

TOM: How can you tell if your car has been hit by lightning? Well, if the headlights are permanently fused in the “on” position, that's a good indicator.

RAY: Or if you start discovering, during the next few days and weeks, that other electronic components no longer function, or function incorrectly.

TOM: Or if there's a huge pile of charred steel and smoke where the car used to be. That's a hint that even my brother would pick up on.

RAY: I don't think your uncle's car took a direct hit, Shannon, but obviously there was some high voltage very close to the car. My guess is that somehow, the headlight relay got energized, and its contacts melted and fused together, so it could not be disengaged by the switch.

TOM: I'd guess that replacing the headlight relay will allow you to operate the headlights normally again. The question is: Was anything else affected?

RAY: The worst-case scenario (other than the above-mentioned charred heap of smoking steel) is that the voltage surge fried your computer and some wiring harnesses. That would keep the car from running at all, and would be expensive to repair.

TOM: But there are plenty of other, smaller insults that can be caused by proximate lightning. So have Unc test all of his lights, blinkers, accessories, etc. And make sure he can still get the Frank Sinatra station on his AM radio (we know 2001 Town Cars come hardwired to that station from the factory). Good luck, Shannon!

You can listen to Tom and Ray Magliozzi’s “Car Talk” program at 10 a.m. Saturdays on National Public Radio station WUSF, 89.7 FM.

Got a question about cars? E-mail Click and Clack by visiting the Car Talk website at www.cartalk.com. They can’t answer your letter personally but will run the best letters in the column.

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