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if sitting in the sun on a hot day, my family's 1995 Mazda protege 323's headlights will come on, even though they are not switched on. This occurs with the car off, and the keys out. The simple way to turn them off is to disconnect the battery, as repeated use of the light switch has no effect. Once the car interior cools down, the battery can be reconnected and the problem is resolved until next time it is sitting in the sun (with windows up). I called a local auto electrics shop who claimed to have never heard of this problem before. Any ideas?

  • I have never heard of that before, good question! – Max Goodridge Jan 7 '16 at 21:17
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    Is it the main or dipped beam? – HandyHowie Jan 7 '16 at 21:41
  • Does this happen if the windows are left open? (IOW: Wondering if heat buildup inside the car is causing this to happen or if it is just an overall "heat on the car" thing.) – Pᴀᴜʟsᴛᴇʀ2 Jan 7 '16 at 21:46
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    Has the light switch recall been performed? NHTSA Camp.# 00V118000 Not the same symptom but a known faulty part and free if in the USA. – Fred Wilson Jan 7 '16 at 21:56
  • low beam (as we call it in Australia), I think. – Michael Wilson Jan 8 '16 at 1:20
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Possible culprits:

  • A bad headlight relay

    Have the relay tested or replaced. It could be that the switch for the main circuit is intermittently stuck-closed.

  • A closed-circuit in the light switch or relay getting grounded

    Eliminating a bad relay would leave you the possibility that the relay is being activated when it shouldn't through an intermittent closed-circuit.


Could sunlight cause an intermittent closed-circuit?

Perhaps heat is a more relevant player here. The thermal expansion of wires could be responsible for the intermittent behavior that is observed here.

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    Easy troubleshooting step: remove the relay and see if it still happens. If not, then you only need to look at the relay and back to the switch. Otherwise, it's between the relay and the headlight assembly. – Edward Jan 7 '16 at 22:11
  • good thinking. I will attempt to do this, although to be honest I don't know where to look for the relay........ – Michael Wilson Jan 8 '16 at 1:26
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    The relay panel is under the bonnet on the left side of the car between the battery and the suspension strut attachment, in a plastic box almost as wide as the battery. The box cover will be designed for easy removal, either with spring catches or easy screws. – A. I. Breveleri Jan 8 '16 at 2:44
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If your alarm flashes the headlights, then the electronics in the alarm could also be at fault.

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