7.4 mercruiser alternator

[Cobalt32]

my alternator is only charging slightly over 12volts it has been just below 14 previously. Batts are brand new. Thinking about installing new alternator and was thinking about installing a higher output amp unit. Any thoughts?

 

[Scott Danforth]

if you go higher output, you need to re-wire

 

[alldodge]

alternator is only charging slightly over 12volts it has been just below 14 previously

Would be either a wire has become disconnected or alternator needs fixed. Before you look to replace, check the back of the ALT for voltage. The Red/Purple small wire and the Orange wire on larger post should have 12V with the ignition ON or OFF.

Next check the Purple wire for 12V when the key is turned ON

 

[Cobalt32]

Two days before I took her out I did some work on the boat and noticed I had left the batt switch on, been a month since I had taken the boat out. It did crank ok but I decided to charge the batt anyway. I install a slow charge for several ours and was reading 75% charge. Could the batts been nearly fully charged is why the volts read low while running. Not start up issues?

 

[alldodge]

slow charge for several ours and was reading 75% charge

If this means several hours as in more then 8 of so hours and you only showed 75%, then I believe you need a new battery

 

[Cobalt32]

No only about 2 hrs. These are two brand new Monster marine batts. Can’t imagine they are the issue. But? The alt. Is the original 1993 so I’m going there first. About the only old bolt on item left I haven’t changed.

 

[cableguy1979]

Be sure to check the voltage at the alternator. You could have a bad gauge or a number of other things wrong. Hate for you to spend unneeded money.

 

[Mischief Managed]

The vast majority of the time an alternator fails, it's just the brushes that are worn out. You can usually buy new brushes for <30 bucks and they are very easy to install. I keep a spare set on my boat.