The gray part labeled "Lucas 84987 B 0499" is an ignition control module, specifically a PRW-2 model used in some Nissan and Infiniti vehicles. It manages the ignition timing and spark generation for the engine. Function: Controls the charging and discharging of the ignition coil. Compatibility: Commonly found in 1990s Nissan models like the 300ZX, Maxima, and Sentra. Benefit of Upgrade: Upgrading to a PRW-2 can provide a smoother idle and quicker throttle response. Alternative Part Numbers: It may also be listed under part numbers 22020-71J00 or 22020-0B000. Transistor: The PRW-2 uses a newer and faster transistor.