Hi! My 2008, V8 Pathfinder that just rolled over to 200,000 is having some weird issues. Over the last four years I have ended up with a new battery each year and an alternator almost every other year. I am not the brightest bulb in the box but I do know there is more at play with my car. Currently I own a brand new Interstate Battery, a two year old alternator (that tested good), and my headlights and instrument panel “pulse” or to some “flicker”.
HELP! Do I have a relay problem? Belt? I am at a loss and this Pathfinder is my BABY!!!

I would check the earth straps as this sounds like it is struggling to find a good earth and shorting the alternators out.

Check the earth leads from the battery first and then work your way through the engine and engine bay.
You can always put additional earth straps into the vehicle to supplement what is already there to ensure the current is finding its way back to earth effectively