New to boating. How do I charge with an on board charger.  Is it just plug and charge? If so, why does the charger lights not come on when I plug it in? It is a  Guest charge pro 10/3/10 amp 12volt charger. Thanx.

Typically with on board chargers you just plug them in and they charge. Not familiar with your brand or the age of it either. Most newer on board chargers have three lights. One that indicates you have power when you plug it in, one that indicates you are charging at your max amps rating and one that indicates the batteries are fully charged and it is now on trickle charge rate. When I plug mine in after use the power light comes on along with the charging light. Once the batteries are fully charged, the charges senses this and then shuts off the max rate charger and turns on the "go fish" light meaning the batteries a fully charged. At the same time it now switches to the trickle charge rate, so you don't boil all the water out of your batteries.

If no lights come on when you plug it in, I would first check your power supply, which I am sure you already have.  You might want to check and see if your charger has some sort of "overload" switch kind of like and electrical breaker that needs to be reset.  If your power supply is good more than likely you have a problem with your charger.  Take it somewhere and have it checked out.

I would think the light should come on but to see if it's charging, if you have a digital voltmeter, connect it across one of the batteries before plugging in the charger.  It should read something less than 12.8 volts DC.  Leaving the meter connected, plug in your charger, the voltage should increase to over 13.8 and should go to over 14 or 15.  If it does not increase, the charger is not working.   Check each battery the charger is connected to and make sure they are all charging.  

The above post is pretty much right but I don't think the Quest charger goes into the float (trickle) mode.  I too am not real familiar with them since I only run ProMariner chargers but I think the Quest cuts the charger off and then back on when the battery voltage drops to a preset level.