A Cooked Relay Leads to Frazzled Nerves

Dear Car Talk

Dear Car Talk | Jan 03, 2017

Dear Car Talk:

Recently, we left the keys in the "on" position overnight in our 1995 Mitsubishi Montero. The next day, the battery was drawn down to the point that the car would not start. I hooked up my battery charger, which has two boost levels. At the low level, it still cranked poorly. I switched to a 150-amp boost and had my wife crank the engine. The car started right up.

However, now the warning signal that sounds when you leave the headlights on or the keys in the ignition goes off as soon as you open the door, and continuously when you start and run the engine. It does stop when the door is closed and the key is not inserted. There appears to be no other problems. The instrument-panel lights operate normally. The car drives normally, but that constant "peeeeeeeeeeeeeeee" can get a bit annoying. Do you have any idea of what happened and what should be done? My wife doesn't want to just throw money at this noise until we have an idea of what kind of job it might be. Thanks for your help. -- Terry

I can tell you how to stop it, Terry. Take a 2-foot piece of 3/8-inch rubber tubing, and get your head under the dashboard while the buzzer is sounding. Using the tubing like a stethoscope, put one of end of the tubing in your ear, and move the other end around under the dashboard until you find the little relay that makes the noise. It's up under the dash somewhere.

When you find it, unplug it, pull it out and step on it. That'll stop the noise.

I'm guessing that when you left the key in the "on" position all night, a door was ajar -- or the switch on the door frame that tells the car the door is closed is failing -- and that buzzer stayed on all night. And it cooked the relay: That relay got so hot that it welded itself in the "on" position.

I don't know if that relay also serves any other functions. After you remove it, you may find out. If you notice that something else stops working -- like your headlights -- then you'll need to replace the relay. So don't stomp on it after you remove it; hang on to it so you can take it to your auto-parts store (or your favorite online parts supplier) and match it.

If the relay is exclusively for the warning buzzer in that car, then you can just take it out and leave it out if you want to. Just remember, it's then incumbent upon you to notice if you're driving around with the door open.


Get the Car Talk Newsletter