Hi guys, I have a 2001 F-150 4.2L 2WD. Recently I have begun to notice that all the lights on my truck have started to pulsate ( e-brake light, dash lights, healdights, parking, interior, DRL, brake and reverse), in the past week or so the intensity has increased a great deal. This issue only occurs when the engine is running. I've check all the ground connections, had the alternator tested a couple different times and I'm kind of lost here. I did put a set of aftermarket projector headlights on the truck with HiD bulbs, but that has been a couple months ago and its just been the past 2 weeks that this issue has started. I may be wrong but I'm leaning toward either the headlight switch, possibly need a new battery (even though it tested good) or maybe that the voltage regulator in the alternator is going out even though the alternator tests good. It doesn't speed up with engine speed when I rev it up, it just stays constant at the same rhythm. I don't want or have a lot of money to waste guessing so any help you can provide is greatly appreciated.
Thanks

 

Bad diode in the alternator, or a bad battery

 

I was figuring that the alternator was more than likely the culprit, it has a duralast gold on it so it should be easy enough to just go to autozone and swap it out