I have an '08 3500 w/6.7L Cummins. It has the dual battery set up.

Can anyone tell me how they are connected?

Are they just wired in parallel or is there an isolator of some kind between them?

If I wanted to store the truck with a battery tender attached, which battery would I attach it to? Would it charge both batteries?

Thanks in advance for any insight, I've yet to invest in a shop manual.

 

they are attached it parallel, hook up to one and it will charge both, no isolator

 

Thank you!!!!