QUESTION: Replacing headlight bulb, 91 Sentra?

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Well first you should disconnect the negative end of the battery (You don't have to though), then find the electric plug, and you should press down the clip and pull it out to disconnect the power to the light bulb. After that you should rotate the ring counterclockwise that's holding the light bulb in place. After that just slide the old light bulb out and put the new light bulb in, then put everything back together. At least that's what I did for my 2003 SE-R, I'm not sure if they all use hte same housing for the lights.