What could be causing this Plymouth Laser to start automatically?

Dear Car Talk

Dear Car Talk | Mar 01, 2005

Dear Tom and Ray:

Our 1990 Plymouth Laser starts automatically. It has happened twice: once in the rain in the middle of the night, and once in sunshine in the middle of the day. When this happens, we cannot shut it off with the ignition key, and we have to pull the ignition fuse. Why does this happen? -- Randy

TOM: It might be trying to run away from home, Randy. Do you wash it enough?

RAY: This car has something called an auto-shutdown relay, and I think that's your problem. Rather than route a huge amount of electricity through the ignition switch on your steering wheel, the electricity to run the car goes through a relay instead, which is safely on the engine side of the firewall. So, when you turn the key to the "start" position, you're actually energizing that relay. For some reason, the relay in your Laser is energizing itself.

TOM: On a 15-year-old car, it could be malfunctioning for any number of reasons. It could be rusty, it could have water in it, or it could just be worn out.

RAY: On most cars, the starter relay would simply cause the car to crank until the battery was dead -- which wouldn't take long. But because you have this auto-shutdown relay, the relay can actually allow the car to run, as it energizes the coil, too. Thatwhat I think is happening.

TOM: Ask your mechanic to replace the relay, and I think you'll be able to sleep soundly at night, Randy -- and, like I do, during the day, too.

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