So its a Belgium made 1988, rope start, longshaft 9.9hp with an AC lighting coil.
Note that that the socket has three wires and was intended for lights wired in a series parallel configuration which is described in the owners manual
However there is, or at least was, a battery charging kit that plugged into the socket.
You will find it in the accessories section of the BRP parts catalog as part number 0582105 You will also find a breakdown of the kit into its component parts
http://epc.brp.com/Index.aspx?lang=E...b-0c4def8640e7
I suggest you contact Oakley Marine in Brighton
http://www.outboards-direct.co.uk/ to see if the kit is still avaialble and if so how much it will cost.
( It should avaialble. MRSP in USA ia $91)
Probably a less expensive option is to simply buy the 4 wire rectifier, part number 0581778 and associated terminal strip fit it directly onto the power head and wire it up like it would be in an electric start engine but simply lead the DC cable out via a suitable grommet. This is how I would do it if possible and it is how my 6 hp Yachtwin is wired as standard.
There should also be a plug available that fits the socket should you wish to try some alternative. I dont know the part number but Oakley will no doubt be able to help.
Remember though an ordinary bridge rectifier is not suitable for the three wire output, You could if you are into electronics make up a ( 3 phase) rectifier with 6 suitable diodes.
BTW you should be able to find practically everything you will ever need to know about your engine in
http://www.leeroysramblings.com/