help with battery isolator install

[Spanish#007]

I'm trying to in stall a battery isolator on 140 horsepower Evinrude outboard I got two batterie! I'm not trying to integrate a switch I just want to hook up the isolator. What I found is that the same Cable that charges the battery is also used to start the motor? the wire splits right before the solenoid looks like I could tap into the charging wire which I believe is the smaller of the two, problem with that is I don't want to run a wire from my outboard I'd rather want to wire somewhere else if possible I've got my trim box in a perfect place to do this I'm just not sure if that would work, the other possibility but I'm not sure would work is if I could take the main cable for the starting battery, the positive cable that charge the battery and sends charged to the starter and hook it to the middle post of the battery isolator then connect the positive cable from each battery to the other two post and connect all negative together. It seems like this would work but also seems like it would then be both batteries that would be starting the motor I'm not sure if this would hurt anything if it wouldn't I may just go this route. My main concern is that I will always have charge to start the battery, I have everything but starter and trim running off house battery. Other concern is whether the stator has enough power to charge both batteries although I realize I'll have to charge them every once in a while, right now its before every trip out. Thx in advance
I can post a pic of the wiring if needed

 

[Spanish#007]

Re: help with battery isolator install

I'm trying to in stall a battery isolator on 140 horsepower Evinrude outboard I got two batterie! I'm not trying to integrate a switch I just want to hook up the isolator. What I found is that the same Cable that charges the battery is also used to start the motor? the wire splits right before the solenoid looks like I could tap into the charging wire which I believe is the smaller of the two, problem with that is I don't want to run a wire from my outboard I'd rather want to wire somewhere else if possible I've got my trim box in a perfect place to do this I'm just not sure if that would work, the other possibility but I'm not sure would work is if I could take the main cable for the starting battery, the positive cable that charge the battery and sends charged to the starter and hook it to the middle post of the battery isolator then connect the positive cable from each battery to the other two post and connect all negative together. It seems like this would work but also seems like it would then be both batteries that would be starting the motor I'm not sure if this would hurt anything if it wouldn't I may just go this route. My main concern is that I will always have charge to start the battery, I have everything but starter and trim running off house battery. Other concern is whether the stator has enough power to charge both batteries although I realize I'll have to charge them every once in a while, right now its before every trip out. Thx in advance
I can post a pic of the wiring if needed

now that I think about it I don't think be able to put starter/battery cable on the middle prong of the isolator I'm thinking the diodes will only let the current charge the battery it shouldn't let current start the boat set up that way, correct??? still wondering if I can run something off Trim Box though?