Convertor/Charger Question

[67 Goat]

I am having trouble with my coach batts boiling dry. Is there a way to check the charger on my 1978 Newell? It is rated at 70 Amp. I am running 3 12V deep cycle batteries that are less than 1 yr old. It has boiled 1 or 2 cells dry on each batt. I'm thinking of updating the charger. I noticed that the positive lead coming out of the charger terminates at a block. There are 2 smaller wires coming out of that block. Is that component necessary? Should I just hook the positive lead from the new charger to that block just as the old one is?

Thanks,
Dean