1993 mercruiser 4.3 stopped running on the lake (electrical)

[NCrunner2012]

Ok background. New to me boat (I know, typical). Went for a cruise, noticed the voltage was low between 10-11while running. Stopped to swim, had a hard time getting it to start. Slow turning like low battery.

I switched to another battery and fired up. I knew there was a problem so I headed back to the boat ramp, but before I made it the boat shut off like I switched the ignition off. There was no power to the dash. I popped the hood and realized that the main orange wire to the alt has broken off.

So now I'm thinking that the batteries are dead because the alternator was not charging. We waited for a jump start, but before the guy came back it started up again. Every time I tried to speed it up to get home it would cut out and I would lose all power.

Finally made it back and got it home. I have fixed the alternator orange wire with a new connector. I obviously know that was a problem, but why would the ignition cut in and out (trim and other things worked fine). It seems to me the ignition switch might be on the fritz too.

Could the alternator being disconnected cause the ignition to act up?

I'm just confused because I would have expected the batteries to be drained, but they were at 12.8 volts.

Can anyone explain two fully charged batteries with a disconnected alternator?

 

[Silvertip]

With no load a battery may very well show 12 volts. Put a load on the battery and voltage drops like a rock. In short -- you do not have two fully charged batteries. Since you ran with the alternator disconnected you may be in the market for a new alternator.

 

[Scott Danforth]

Have the batteries tested