Batteries Overcharging

I had to take my boat off the water early today due to my volt meter indicating 18 volts, engine is a '06 F150 TXR. Without the eng running the digital multi-meter on the batts read 12.8 volts each individually. Started the eng on each batt individually and each read 13.7 with eng running. However, each eng run test the volt meter read 18 volts, the eng was at idol. Not sure if its important the tach is working and follows throttle input. Is there a better way to test the rectifier/regulator and/or gauge?

Hmmm 18V is very high, you expect between 13.8V and 14.2V to be coming from the regulator. Can I just confirm, when you refer to the volt meter that reads 18V, is this the same multimeter you tested the battery with or the volt meter on the dash?

Stuart

Thanks for the reply and I can see where it could seem a little confusing, yes the 18 volt reading was always at the Faria combo fuel/volt gauge. So, as a follow-up, checked/cleaned grounds as needed up to the boats Faria combo fuel/volt gauge, ran the motor, Faria volt meter 18 volts. Removed gauge disconnected volt lead from gauge, connected multi-meter to volt lead wire and grounded to the gauge post, started engine multi-meter read 13.7, put load on it 13.7-14 VDC ... yeah! Have come to the conclusion that I don't like comb gauges. Now I have to buy this gauge for the volt meter knowing my fuel level probe is bad, but a lot better than buying a rectifier/regulator.

if the actual voltage was correct it should not have damaged the probe...

Your voltage regulator is dead. Get ready to buy a new rectifier/regulator.