THERE ARE BASICALLY 4 DIFFERENT SYSTEMS THAT ARE ADJUSTABLE BY THE OWNER.
TO DETERMINE IF THE 89-90 9000s HAVE BEEN UPDATED TO THE LATER ECU, REMOVE AND REPLACE FUSE 22 IN EARLY 89s AND FUSE 19 IN ALL OTHERS UP TO 92, THE LED IN THE LEFT SPEAKER GRILL SHOULD FLASH 4 TIMES AFTER FUSE IS REINSTALLED. AFTER IT FLASHES, CLOSE ALL DOORS, BONNET AND BOOT, TURN KEY IN DRIVER'S LOCK TO UNLOCK AND HOLD FOR 10 SECS.
IF NOTHING HAPPENS, YOU HAVE THE EARLY ECU.
IF YOU HAVE THE SECOND ECU, THE SIREN WILL CHIRP AND THE PARKING LIGHTS WILL FLASH. THE NEWER ECU WAS RETROFITTABLE TO THE EARLY CARS TO ENHANCE THEIR PERFORMANCE.
THERE WAS A FURTHER REVISION AFTER THIS ECU TO ANOTHER THAT WAS USED UNTIL 1995MY. IT INCORPORATES FUNCTIONS TO RETAIN THE SETTINGS IN THE EVENT OF LOSS OF BATTERY POWER. IT WILL RETROFIT TO THE 89 AND 90 MODELS AS WELL. IF THE CAR IS EQUIPPED WITH IT, THE ALARM WILL REARM AT THE PREVIOUS PROGRAM LEVELS UPON POWER RESTORATION AND NORMAL ALARM ARMING.
(NOTE: On 9000s, the ECU must be securely fastened to its bracket to prevent false alarms. It lives under the dash on the right side. Remove the glove box to access it. It slides in from the front to the rear of the bracket, locking into tabs on the bracket. The first 2 ECUs are black boxes about 4X4 inches. The last one is the same size but yellow.)