Why Does My Headlights Flicker When I Drive?


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Here are a few suggestions: 1.  Check your battery cable connections at the battery.  Take them off and clean the cables and the Battery terminals with a wire brush (you can buy a Battery Terminal cleaner brush at any auto parts store for a few dollars.)  Put a little di-electric grease on the terminals and bolt them back on.  If you can move them by hand they are either not tight enough or you need new cable ends.  This is the easiest fix.  
2.  Alternator diodes could be going out - the diode cuts out the negative side of the AC current (alternating current) that your alternator puts out, this is necessary because your vehicle uses DC current.  If you have AC voltage in your system it can cause light flickering and  eventually other problems.  If you have a voltmeter, set it to "AC volts" and with the engine running put your red lead (from voltmeter) onto the big fat wire on your alternator (positive from Battery).  Put the negative/black lead on the alternator case or negative side of battery.  If your alternator is putting out more than 0.055 volts (AC) your diodes are probably going out.  Time for a new alternator or a rebuild.  3.  You could have a bad connection between the voltage regulator on your car and the alternator giving your alternator a false signal so it puts out too much voltage.

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