Question about 2000 Mercury Grand Marquis

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2000 Mercury G/Marq - After approx 45 mins of the car running, the headlights will start to flash. We've replaced the hlight switch and still does it. Any Suggestions ??

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Yes, I suggest looking for the Headlight Relay and a Circuit Breaker. You should find the Relay in the Powerbox under the hood and the circuit breaker should be in the fuse panel.

What is happening is the contacts are overheating. Instead of blowing a fuse some models use a Circuit breaker which recycles when it cools down. You can get the same action out of a Relay that is going bad.

If this continues after you replace the parts you should test the voltage going to the headlights and check the bulb sockets for corrosion. The headlights are made so that the low beam and high beam are separate and they are not on at the same time. If both filaments were on at the same time it would overload the relays and the Circuit breaker.

You will see that the bulbs are rated with 2 numbers, like 45/65 for low and high beam. If one side shorts out it will pull an additional 65 watts. Instead of drawing 90 total on low and 130 on high for 2 headlights, it will pull 155 with 1 headlight shorted. Thats 25 watts more than the Relay or Circuit breaker is suppose to handle. After 45 minutes of this, you get the flashing.

Posted on Nov 13, 2010


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