I have a 2004 F250. %.4 gas and 6 speed. The alternator is 15 months old. Ithe dash light comes on. I pulled over and checked the voltage. It was 14.2 volts. i got home ( 2 miles) engine off voltage was 12.9 engine on voltage was 14.3. Is this okay. THANKS.

 

12.9 V is battery voltage without charging.
Weak point on those alternators is the control plug, other than that I replaced rebuild alternator 2 months after buying it.Had the blinking light from day 2, but the alternator passed bench test, before it gave up 2 months later. Good luck.