Over the weekend I noticed when i was trimming up the radio would shut off? then come back on? then noticed my volt gauge read 11.5v-12v while under way . When I got home I put a volt meter on the battery while running and it read 12.4 volts, is this to low? my first thought was was bad ground?

I'm no mechanic but if you put a meter on the battery while motor is running you'll get a pretty good idea if its the altenator. should be 14 atleat, motor off your checking the battery, 12.4 is low.

motor off was 11.8, motor on was 12.4? i thought that was low also, could it be anything else?

should be aprox 13.8 running

Full charged battery is 12.7 Depends on your volt meter as to what you see. Take your volt meter & put on your car/truck. Running voltage should be aprox. 13.8 volts, sometimes it will be higher & sometime lower. This will give you a good idea of what your meter is readiing. I would say your alt. needs to be replaced if the numbers you are giving is correct. Before you buy a new one have the one you have checked out first. Could also be a ground problem.

Could very likely be a bad battery. Alternators should produce about 13.8 volts under normal conditions however if the batery is sucking up current (amps) flow (voltage) will decrease. You can't make alot of current and maintain voltage at the same time, the higher the voltage reading is the more charge the battery has in it. Although the bit about the stereo cutting out during trim operation points to an alternator. It's just a little odd becuase your alternatot is producing some power which is evident by the increased voltage while running. Ussualy when an alternator fails it fails completley and does nothing, but not always. Take em both out and have em tested.

The way I used to check to see if I had a bad alternator was disconnect the battery while the boat was running and if it died that meant the alternator was bad. If it kept running alternator was good. But I also heard not to do that on computerized engines.

I had the same problem and it was a bad battery. I was running two batteries and the good one covered at normal loads but the trim and radio would kill both of them.

I would 1st try the simplest: pull the battery out and do a full load check on the battery, along with a volt check by cell if a non-sealed unit and voltage drop test on grounds and positive leads.

If battery has failed, install new and retest charging system output.

Mine does the exact same thing.
I've got a new battery and all. Did it with the old battery too. I've cleaned all the connections and it still charges at 12V or less.
I'll pull it this winter and have a local rebuild shop look at it.