Random overcharging issue

Looking for some help from the Tundras hive mind. Got a 2009 5.7L that randomly overcharges the battery to 17+V. The entire dash lights up, headlights get brighter (and burns out the bulbs without blowing any fuses), but truck drives just fine. It lasts about 3 seconds and then goes back to normal.

• I have torn the dash, doors, kick panels, and door sills apart to look for water ingress only to find none.
• I replaced the battery with a new one, and it happened again 1,000 miles later. (So, I’m ruling out the battery.)
• A new alternator is on the way, but the extremely rare and random way it overcharges makes me think it’s not the alternator. I could be wrong, though.

Any other possibilities? Does this issue sound remotely familiar to anyone?

I have checked voltage with a multimeter. Multimeter reading matches the dash gauge, which stays put 99.99% of the time, except when it surges to over 17 volts.

I hate electrical issues.

 

Is the regulator built in to the alternator? Or external? I would lean toward built in because that’s whats I’ve seen on most modern vehicles, but I’ve not had to deal with an alternator on my truck yet.

I would suspect the regulator is bad, the circuit is grounding in the alternator somewhere, or you possibly have a bad/corroded wire on or around the alternator causing some mayhem.

I’d replace the alternator and have the old one tested. Check the wiring around it while you are in there. I’m told that the alternator is kind of a PITA to swap, so good luck. Hah.

 

It’s a huge PITA to swap. Only time I wish I drove a Chevy.

It just arrived, so I’m gonna start on it tomorrow. Thankful for unseasonably warm weather!