The 2 post switches will work the same with only 1 wire attached. They simply provide a ground on the yellow wire so the interior courtesy light comes on. That other wire provided a ground to a courtesy lamp delay timer that would keep the interior lit after the door is closed. Either a time period or until the ignition switch rotated to on position canceling the delay. It's a nice option for ladies seeking keys in their purse/piece of luggage but,,, These delay timers would die in their closed position. Walk away from the vehicle and interior light never goes off, battery drains. New delay timer simply plugs in like a oversized flasher. So... retain this optional equipment or delete it? Your choice
