Like the other post says the bulb out relay works with voltage differential. That means the lights on both sides must conduct electricity the equally. Barring the
relay being bad that is. So, if the light on the other side of the car hasn't had it's connecter and cirucuit board contacts cleaned. A new light and an old light
will not conduct equally. This turns on the bulbout light. Try some plastic safe contact cleaner from an auto store. I also use some grit cloth on the contacts but rub very lightly as the conductor is very thin copper on plastic. Also this circuit card is available separately new for about $20. It's pretty easy to install and that surely makes current flow well. Also make sure the ground wire
on the lamp assembly is connected to ground. It connects with a screw to the inside metal panel in the trunk.

Dave 82 242ti 277k mi.