RV Repair: Battery connection, battery connection, ground wires

Question
Hi Thom!

We purchased (2)new batteries for our travel trailer.We're thinking we might have connected them wrong as they are not charging properly.  There are 2 white wires (1 is bigger than the other)and the red and black. Can you please help????
Thank you!!!

Answer
Hi there...
White wires are ground wires ...black can sometimes be ground but is more than likely a 12 positive ..Red is always 12 positive. The big white wire is the ground to the trailer, the small one is the interconnect between the two batteries.

Thom