I bought my 2006 after an indie had done some charging system work, including an alternator and battery. The PO had to take it back and they replaced the alternator again. I then bought it and it had an overvoltage code (don't recall what it was, but I posted it and you could probably search and find it). IIRC, I was getting high 14's from my multimeter. Napa replaced it again (third time) and that time it stuck. It was this one: https://www.napaonline.com/en/p/RAY2136830 Even if you don't have the same one, I'd take it back. I did not have the same issue on the dash that your son has but I could see running it that high could cause issues like that, which will probably need to be addressed separately per all the above help.

 

It was the alternator and it's back at the shop that put it in for him. I got my figures crossed as that is the problem.

 

Yeah, lets see how it is after the swap. I have had bad luck with alternators also. I think it was my BMW that took three alternators to get a good working. The first rebuilt was bad upon install, the second failed within a couple weeks I think. Third lasted years. It is really frustrating. Now I have an LR OEM unit sitting on a shelf for next time. But if you keep the old ones, they are pretty easy to rebuild. I have a couple cores on hand for the day I finally get around to it.

 

wirh the last one I returned (didn’t have the history on the first two), the alternator worked great at 15v. It think it was the regulator/rectifier that was the issue. If Napa hadn’t replaced the whole thing, I was tempted to replace that part only and see if that fixed it. I think it was like $30.

since the OP’s title is this only happens when cold (and more juice from the alternator?), hopefully the new one solves his issue