Either you replace the 12V alternator into a 24 V alternator and step down to a 12 V system where needed. Or you get a replacement 12V winch motor which will be cheaper in the long run.

 

What ^^^ said. That winch battery is gonna get wrecked pretty quickly if you go try to go with the three battery set-up. You'll need to convert something to make your winch work properly. Do you plan on using a ****** block with that winch? If not, look into getting one. That's a whole lot of truck for a 12k winch if you get good and buried.

 

I really like this idea but, I have the same problem. My winch is an industrial 18 (18000 lb.) Is there a way to set up switches using this method to run the winch and then switch them back open to charge the third battery? I cannot change my winch motor over to a 12v motor. Or, do you know of a way to add a 24v alternator seperately on a 94 f-350?