My civic broke down, so I borrowed my sons 05 and his headlights are pulsating. Anyone ever have this problem? What could it be? I've seen quite a few threads but not one with a fix. I've seen grounds, voltage regulator, alternator, and batteries and possibilities. But no fixes.

 

Voltage regulator / rectifier would be my #1 choice, take some measurements with a multi-meter of the battery while car is off and running.

Taking the Alternator off is pretty easy and most places here would test it for free if you bring it to them.

 

Thanks i'll give it a try.