What you have there is, to be blunt, crap. I would suggest to upgrade all of your 12V wiring from your new batteries back to the 12V distribution point. You do not want the frame connected to the (+) phase of the 12V system, matters not how lighting and devices work. You will need a fuse or circuit breaker within 18" of the (+) terminal of the battery that will handle all the loads of your 12V system and some headroom (25% is a good target). This fuse is a catastrophic protection in case of short. The ground terminal of the new batteries would be connected to frame and a cable used that will match the size of the (+) phase of the 12V system, not a 14 ga wire.
Read a little over here, at
Jack and Dan Meyer's website.
