I'm still a little confused. Normally, the reason why one of your batteries has thick cables is to handle the high amp load from the starter motor. However, in a "1-2-off-both" switch all battery cables should be able to handle very high loads. That's the very point of the switch. The cables coming from the switch should go to the + battery posts. Still, a diagram would help. You can fax me one to +30-210-6899133.