So I have a relay that is rated for 12V DC 30 amp. It will be running a couple of things; probably about a 5 amp draw. What I don't want is for those items to draw from the main battery. The button I am using is already power something off of the main battery, and I would like to use that same button to activate the relay, but I want that relay to power my other items off of a separate power supply.
I think this should work, but I just wanted to double check with others before I implement this. 
Sorry about the diagram; the button wasn't saved. The button will be between the top battery positive terminal and 85 on the relay.
