Mercury Outboard Wiring Question

[Brylk1830]

(I also posted this in the electronics forum; not sure which one is more appropriate?)

Hello all,

For the past month I have been doing some research about boating electrical, and although I've come a long way, I have a few more basic questions left

I'm preparing to use two 12v batteries connected in parallel and in such a way as to isolate my starting and house battery. After searching around a bit at the different methods available I narrowed it down between a battery selector switch or an automatic charging relay such as: http://www.westmarine.com/webapp/wcs...classNum=12106

Each of these devices, the selector switch and relay, get wired in a bit different but I have the same basic questions regarding both.

#1.) For the selector switch I can see by looking at the wiring diagrams that it needs to be wired into the starter; I understand how to make connections to and from the battery and bus/fuse panel but I am not sure how to make connections to the engine?
#2.) I've also seen diagrams where each negative of the batteries needs to be grounded to the engine; How exactly do I ground the cables to the engine?

Just by looking at my outboard (Mercury 40 horse 1999 3 cylin) I followed a large black wire from the starter that has a marking to connect it to the batt neg. Also, there is a wire connected to the solenoid that is suppose to be connected to the batt pos.
#3.) The most confusing thing that's bending my confidence is that I cannot seem to find my outboard's alternator? I know the system is hooked up so my starting battery gets charged while the motor is running but I can't seem to find the alternator itself & if I need to connect to the alternator, to wire in an isolater for example, it would be nice to know where it is!
#4.) Lastly, for switches that need to be wired in with the igniton switch is that going to be the large wire running into my throttle?

Thanks a lot for any suggestions/explanations, I appreciate any help I can get!

These are the specs for my alternator: