if he has a LED adapter or LED compatible board in the game where the feature lamp bus is floating adding resistors won't help unless he does every single lamp ore removes the LED adapter board and goes back to stock.
When the feature lamp bus is floating on the LED boards ground then gets a path between two resistors on the LED board letting lamps dimmly glow when they should be off.
This is more than likely why the OP is seeing some lamps come on dimmly when they shouldn't. I can't think of any other scenario that would do it unless maybe some crazy ground potential issues where the LDB is at different ground than the feature lamp bus is.