Ok, so my son's 2001 ranger has the 4 liter v6. We purchased it in March or this year, 2024. It's been an ok truck, basic age issues, that are getting sorted out. My newest gremlin is in the charging system, I think. I've replaced all six fuel injectors due to one going dead. I have changed out the intake manifold gaskets becuase why not, I was in there. I have also replaced spark plugs and wires. I also have replaced the alternator. As of 10-11-24 I have had to replace the battery due to age amd it wouldnt hold a charge. It was a group 59 with 590 cca, standard 5 year warranty. Now for what ever reason I noticed the headlights and all exterior lights have a small flicker, as does the dash and interior lights. I had the alternator checked, and it passed as well as the battery while on the vehicle. I pulled the alternator and took it in to be bench tested at Autozone and their machine said it was operating properly. I checked it with a volt meter, at the battery, once I got home and it is jumping around alot. Seems to be at 12.87 volts static with the vehicle off, and bounces around while running from 13.8 to 15.78 volts. I am at my whits end as far as electrical goes. Everything seems to test fine, so what am I missing? Any help or ideas are welcome at this point. The link is to the specific alternator that's installed on the truck, it's been installed since May.

https://www.autozone.com/batteries-starting-and-charging/alternator/p/raw-power-alternator-a787972/1269835_0_0?searchText=Alternator

 

First guess would be a bad voltage regulator

 

Well son of a gun, i figured it out. It was a remaned alternator, part of the reason it was so cheap, and the voltage regulator had a plastic burr in the port. Freaking A!!!!! Used the dremmel to clean it up, sealed the connector with a bit of dielectric grease and bam!!!! All is fixed. Howed I find that you ask, completley by chance. I accidentally bumped the connector and it stopped. So I played with it, inspected it, and found the issue. Could of saved myself a while lot of effort if I would have seen that sooner. It was inside the connector housing on the regulator side, in the bottom of the plug. At least I got it lol!!!!