1. You have 4 wires to the step quick connect
2. RED and WHITE should have 12 volt power when the inside wall switch is ON (you have a 1999 model RV). Turning the wall switch OFF kills the power to the step to keep it out.
3. The BROWN does NOT factor in this problem
4. The YELLOW is from the Ignition override. CHECK to make sure that wire is DEAD(no 12 volt) when the KEY is OFF. IF NOT, then that is your problem.
5, Have you done ANY work on the steps recently? (Changed any step parts). Doug