All my lights pulsate when running Headlights, dome light, cluster. It's very faint but noticeable. What are some possible causes of this. 01 XLT, 5.4L extended cab 4x4.

 

Your probably needing a new alternator or battery, maybe both.

Get a multimeter and stick it on the battery. It should be 12.5v when the truck is off, 14.5 with the truck on. If its below 14 with the truck on get your alternator tested at the parts store to confirm it's bad. You can also put a load on the truck when doing this test. Alternators usually go bad around 150,000 from what i've seen.

 

If you have a rather decent sized stereo system it will cause this also as the alternator can not keep up with the amount of current draw on the system. Also Ford Spec is 13.8-14.2 on alternator output. But voltage isnt the important number its the amount of amperage output from the alternator.

 

Sounds to me like a bad voltage regulator (located inside the alternator). The voltage regulator is supposed to prevent rapid changes in voltage that would cause problems like pulsing headlights.

 

My stereo does this to my truck, might have to look more into this

 

Thanks guys!!! I was thinking alternator as well, but it's never hurts to get opinions of others. I've been hear a very faint whine for about a month now. I checked it out today and it was coming from the alternator. Thanks again guys!!