The volt guage on my 1992 F150 is high. It shows around 16 volts at idle. Also as the truck warms up a little, the guage and idle fluctuate...not much but a little. The alternator is brand new. Could the idle and voltage fluctuation be related?
Also, when I turn the radio, lights, blinkers, and AC on, the voltage guage drops to around 10-11 volts. Is this normal?

 

The factory gauge is mostly for decoration.

 

Clean the battery post and all the grounds to see if that helps.