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My '97 Ford F-150 truck has power going to the headlights all the time. The back window light is also suffering from the same problem.

It can't be the relay because it clicks when you play with the 2 ground wires by the driver's headlight, and the lights turns off when the ground is disconnected.

I played with the ground while back and it turned off, then when I had to boost the vehicle the lights came back on and stayed on.

P.S. I changed the cab when it started doing this.

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  • Woah, This is more confusing than interstellar. Clam down , edit the question.
    – Shobin P
    Commented Jun 16, 2015 at 9:20
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    One of your grounds is allowing power to feed back through to light whatever it is you're talking about. Some light bulbs power differently than other systems, where the power goes there directly and when you switch it on, you are actually connecting the ground. If the bulb finds a ground from a different location, it can allow the bulb to light and stay lit. Since I don't really understand your question, I'm leaving this as a comment.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Jun 16, 2015 at 11:24

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There are a couple of possibilities here aside from a bad relay (which appears to have been ruled out by your tests):

  • the light switch has gone bad (stays permanently on)
  • there is an electrical short somewhere in the controller circuit (which the light switch controls) that is bypassing the light switch and always completing the circuit
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