New coach batteries......but 12 volt system is inoperative

[DGBPokes]

I let my 5 year old Interstate 6 volt coach batteries get dry late last fall. In February bought two new batteries. Cleaned the terminals, and installed the batteries. Rig has been in storage till last week. No 12 volt system except when a. engine is running or b. it is connected to shore power.

I have a couple of thoughts and would appreciate feedback:
the cable lugs have large openings and the batteries have threaded bolts rather than post. Although I cleaned them good I worry about the loose fit.
Secondly, my cables are 10 years old, I cleaned the terminals till they shine, but I see corrosion on the strands where they go into the insulation. On the negative cable, it has been about 5 years ago, because the drawer wouldn't open fully I spliced in additional wire to make them longer.

The "bridge" cable between the two batteries is new and make by my Napa dealer, again lugs are to big in my opinion.

Addition information.....rig has a good size solar panel on the roof and it has a wire going to the positive battery terminal

[BFlinn181]

Do you have a battery shut off switch? (salesman switch) Perhaps it's not closing properly. Use a meter or a test light and check for 12 v at every connection from the batteries to the fuse panel. Blown fuse or bad connection, slow, methodical problem solving is the way to solve the problem.