Jrs907 - you have the correct fix.
My Bigfoot is a 1988, and it had no battery or any provisions for one. I installed a complete system, including Solar.
I am curious though, why not and a modern charger/converter? Only about $150. Maybe something like one of these,
Powermax Boondocker Series deck mount 4-stage converter/charger. Very simple to install, and you probably can use your existing fuse panel. I have purchased from
Best Converter several times. They are easy to talk to, sale several types, styles, and brands of converters. They may have a direct conversion charger that will replace what you have.
Wayne
2004.5 Ram SLT LB 3500 DRW Quad Cab 4x4
1988 Bigfoot (C11.5) TC (1900# w/standard equip. per decal), 130 watts solar, 100 AH AGM, Polar Cub A/C, EU2000i Honda
Toad: 91 Zuke