Or... Is your coach equipped with Trik-L-Start or some similar device that charges the Chassis Battery from the Coach's electrical system? If so, then powering up the Coach would cause the Converter to power up every 12VDC load connected to its 12VDC outputs. A cross connection like Trik-L-Start would then send power to the Chassis and you'd be able to see it when you turned the key ON.
I wanted Four-Way Flashers on my '59 Impala. Added a kit that did that, following the instructions. Then I thought it'd be nice to have the Parking Brake Warning Light go on when I stepped on the Brake. Ok, wired that up. Then I learned that even if the Key was OFF, if I turned the Flashers ON with the Brake ON, my Radio would go On-Off-On-Off to the rhythm of the Flashers. There CAN be funny consequences when we add things.