Battery gauge fluctuations

[Wings720]

not likely, get a multi-meter and verify the voltage output directly at battery and also at the alternator output while idling.
if you get fluctuation like it shows on the cluster then either the alternator is goofy, or the alternator cable is goofy or the battery cable or bad ground.
if you do not get the same fluctuation at the battery as you do on the cluster then there is something else going on but I wouldn't dig into that until you verify under the hood.
what was the reason for replacing the battery?

Battery was 6 years old. It died when I forgot to turn it off when I had it in neutral to push it onto lift to change fuel pump lol.

 

[Wings720]

Started here.

 

[Fless]

The really important ground by the firewall is the braided non-insulated one that I drew a red rectangle around. Both ends should be clean and the other end attaches to the back of the block.

 

[Wings720]

I had a hell of a time trying to get back there even with my phone. I'm going to order the replacement tonight and swap it tomorrow.

 

[Doubeleive]

I would check it with a meter rather than throwing money at it. you can get a meter for super cheap at practically any department store, auto parts store, harbor freight.

 

[Wings720]

Ahhh. My concern was even if it reads correct on meter isn’t is possible it’s still causing the fluctuation? It’s not constant so it’s hard to put the meter on it while it’s happening.

 

[Fless]

So get one of these - w/ or w/o USB ports and plug it in to the power port. Verify with a voltmeter that it reads correctly, then monitor it vs the IP gauge.

 

[Doubeleive]

Ahhh. My concern was even if it reads correct on meter isn’t is possible it’s still causing the fluctuation? It’s not constant so it’s hard to put the meter on it while it’s happening.

it's where you should start, regardless k.i.s.s. method
I will add if it is intermittent then the alternator would be my primary suspect

 

[Wings720]

Thank you for the ideas. sorry im not the best mechanic lol. Honestly I used to never do maintenance or diagnosis I would just use the parts cannon after failure.