I have pulled out my old Flyback 20-3 charger and will be replacing with a Xantrex 40A charger. A few aspects of the wiring have left me pondering.

The Flyback had 4 DC wires coming from it. Battery #1(+) terminal on the Flyback (red wire) went to the (+) post of battery #1. Battery #2(+) terminal on the Flyback (red wire) went to the (+) post of battery #2. Negative/Ground terminal on the Flyback had both negative wires (black) connected to it, and those wires went separately to the negative posts on each battery. The only chassis ground that I could find on the Flayback was a small green wire jumping about 2 inches from the chassis to AC ground.

I understand what to do with the positive wires, but the negatives leave me wondering. The Xantrex call for only one negative wire going back to the charger from a common negative for the two batteries. In that both batteries are physically connected post to post at the negatives via a jumper, doesn't that mean that one of the two black wires from the Flyback to each separate negative battery post is unnecessary or redundant? Or, is one negative and one ground? (I'm thinking no on that). If one's negative and one's ground, how could you tell them apart? If neither of the existing black wires is a ground, what to do with the ground on the Xantrex chassis? Install another 4gauge wire and run it to the engine block? Any suggestions on a better (ie easier) place to run that ground if necessary?

Thanks,

Joe Welna