I may be wrong but the solenoid has 2 big terminals and 2 small terminals. 12v on one of the small terminals and ground on the other connects the big terminals together, 12v on the other small terminal and ground on the first small terminal, disconnects the big terminals.
You said earlier that you removed a jumper across the terminals, maybe the solenoid is bad.
Right now on my MH the chassis disconnect relay is bad, I have it jumpered across. If I want to disconnect my chassis battery, I have to remove the ground cable at the battery. It has been this way for almost a year no problems.
06 Hurricane 34FT WH W20 Chassis 8.1L 129K, Steersafe, Koni Shocks, DIY Trac Bar, Tri-Metric 2025RV Battery Monitor, 4-6V Batteries, Scan Gauge 2, Crossfires, 735W Solar Morningstar MPPT-60, KVH R5 In-Motion Sat, XM Radio, 07 Chevy Malibu Maxx Toad, Falcon 2, Brake Buddy, Escapee