Alternator charging but not charging batteries

[gutthooked]

Got a 79 260 mercruiser mc1 with I think is a Motorola 3 wire alternator pertronic electronic ignition. Never had electrical issues until I had the shift cables bellows serviced last fall. The shop that did the work had the trim sensor wired both wire to ground & told me my gauge was bad. My tach seems to be off some now and flips over when started. I don't know if they fiddled with anything else or not. Anyhow this is what I got now 14.62 volts on the back of the alternator 11.6 when engine not running 12.7 with engine running, 13.7 v at the back of gauges. I cleaned up terminal and connections at battery. Charged the batteries and had tested all checked good but have not retested yet. I don't know the serial numbers of engine or outdrive were written down in my manuals that were stolen from boat. Need some ideas on what to check or look for. Would be nice to see the wiring schematic for this engine.
Thanks John

 

[alldodge]

14.62 volts on the back of the alternator
11.6 when engine not running
12.7 with engine running,
13.7 v at the back of gauges.

The 11.6 when motor not running means the battery is basically dead, should be 12.7 fully charged. The tach bouncing and other readings tells me there is a bad ground

Remove the ground lead on the block and clean it. Since the trouble started after the sender work, check to see if a ground wire was left off on the block

 

[gutthooked]

I'll give the ground a try, unfortunately for me the boat is 200 miles away now, so I can only work on it during the weekends.

I forgot to mention had the 25 amp fuse blowed for the fridge when I got the boat back from service. Replaced the fuse and it works fine now.

 

[gutthooked]

Ok cleaned up the battery terminals, ground to block and back of the alternator, found the connection on back of the alternator was bad and fell off after barely touching it. Also tightened up the alternator belt. The batteries are charging up to 13.8 so I guess that what was wrong. Had all of the batteries tested and they were good.

 

[alldodge]

Cool beans, tx for coming back with the solution