25 efi mercury charging question

I have a 25 mercury efi 2005, pull start. Runs like a dream. I have been to 2 different mercury parts dealers and one tohatsu they pretty much say they know nothing about this motor its a tohatsu or when looking up parts, wow I have never seen anything like this. you'll have to bring it in and have a tec look at it... : I have a simple question they can't answer my motor has three fat yellow wires coming out from under the flywheel with a gray plug on the end just hanging there. I assume that's connected to the charging coil. What part or parts do I need to complete the charging system to charge my boats battery's? 
I do realize i will still have to charge at home as well due to
the heavy draw of the trolling motor. I would like to be able to replenish the power used up by other electronics stereo,gps, fish finder, lights ect.. Some days i like to crank up the hank and pole all day...