My Outboard Won't Charge My Battery...Please Help!

[OrangeCrush]

Dear all,

I posted about this a while back, but I thought I would start a new thread with updated information since it was so long ago.

So... I have a 2003 15 hp 2-cycle Mercury outboard. (I could be wrong about the exact year, but that is what the previous owner told me). The battery leads that come out of the motor do not charge my battery. I tested the circuit with a voltmeter and the results were pretty interesting.

When idling, the voltmeter shows voltage fluctuating around 5 or 6 volts. It seems to creep up the longer I let it idle, but it never gets above 8 volts or so. If I put the motor into gear and give it some throttle, the voltage drops to 0.0 volts. Back to neutral, and it will creep up slowly again, fluctuating as it creeps up towards 8 volts. If I reverse the positive and negative leads, I get the same results but with a negative voltage indicated. [I'm not sure if the following piece of information is relevant, but if I only connect the negative lead to the voltmeter, it shows much more voltage, like 20+ volts, fluctuating wildly]

I took off the engine cover and inspected the connections. Everything looks solid. The black and red wires are connected to a little black box mounted on the side of the motor on a metal plate. The red wire comes off a contact on the front of the box, with yellow and white wires on separate contacts that lead elsewhere around the motor. The black wire is connected to a screw on the back of the little black box. This makes sense to me, as it should be the ground.

If you haven't guessed already, my knowledge of electronics is quite limited, but I have all winter to figure this out. I am planning a large trip next year and I need this charging unit to be working correctly... so my questions are the following.

1) Assuming there is something wrong with the motor, what can I do to troubleshoot the problem myself?

2) Assuming I need a manual for this, how can I figure out the exact year and model of the motor, and where can I get a manual for free or cheap?

3) If I need to go about replacing parts on the motor, how can I begin to know what parts need replacing and where to find them?

Thanks a lot for any advice you can give me,

Jack

P.S. I am attaching a photo of the 'little black box' I mentioned in my post. The red line is coming off the bottom corner and the black line can be seen going into the same sheath as the red, and it attaches to the screw that can be seen to the right and slightly behind the little box.