Very thorough analysis before the switch was altered. Basement had three-way switch for overhead basement and stairwell light. The three-way also included a switch by the basement door to the outside. The stairwell light switch now turns on/off the stairwell light and the overhead basement lights. No more trips back down the steps to shut off the overhead basement lights! YAY!
Rewired so that the switch at the top of the stairs controlled the basement light plus stairwell light. Eliminated the three ways switches