EUL/IMS module, found on the back of the instrument cluster in '87-89 V8s.
Extended Useful Life / Inferred Mileage Sensor
http://www.supermotors.net/vehicles/registry/media/544459
Haynes contains a typo in some editions describing this as the "Infrared" Mileage Sensor, and wiring diagram errors showing it connected to the oil pressure switch.
