[pagehughes05cummins]

changed one last week. it seems to out again this week gauge would go 16 and then back to 12 and then back to 16 and stay there most of the day. but yesterday it went to 12 and check gauge light came on and stayed on till i got home. drivers side battery was dead, 07 6.7 cummins

 

[nlneilson]

16 v seems a bit high.

You can do a 'Search' in the forum for 'alternator' for an 07, try this link.
http://www.cumminsforum.com/forum/search.php?searchid=10534197

The voltage regulator is probably in the little computer near the driver side battery.
My alternator was replaced shortly before I bought the Dually so don't have personal knowledge about tinkering with it.