Back in my days as a Chevrolet mechanic in the 60s the charging voltage was always set from generator at 14.2 volts, while monitoring my voltage on Edge Insight I see it jumping from 13.4 to 13.8 but never over 14. I assume this is normal but seems like 14.2 would do a better job of keeping the batteries charged...comments and discussion welcomed.
With my insight I am only seeing 13.3 tops usually 13.1 at hiway speeds, when it first starts I get down to 10.9 while the glow plugs are on. I just replaced the batteries with 2 brand new ones so I don't think its the batteries. Seems I have a the same symptoms as the original poster. Could our alternators not be able to cope with the electrical loads of our trucks?
I just had the same issue. At a stop light, my voltage would drop below 12V. I ended up replacing the alternator. I upgraded to the 140 Amp motorcraft instead of the 110 amp that came on the truck. I am amazed at the things that have stopped working recently... I have 97,000 miles and the truck is an 04.