voltage issue?

Have a 2011 Tundra, had the alternator replaced a couple days ago, was told it was bad. Battery tested ok. Today I noticed that the voltage gauge is fluctuating from 14v to 10-12v approx. dash lights also dimming the getting bright again. Any theories what to look at next?

 

I would look at the battery again. When you tested it, did you have any load on it? Run the ac and stereo to see if rpms fluctuate.

 

Agree with having the battery checked again.
An alternator that has failed normally has worn the battery down while it was failing.

Do you know if the battery was load tested?

 

Make sure the connections at the alternator are all solid and that the cable hasn't been compromised.

 

Sounds like the voltage regulator if the above is good. If it's a reman alternator, a lot of times they reuse the voltage regulator.