From VIN S5220000

"Lights ON" warning chime
Battery voltage is applied through the TAIL fuse to the "Lights ON" input of the electronic time and alarm control module when the light switch is in PARK or HEAD. When any door is opened, its door switch applies ground to the "Door open" input. If the "Door open" input is grounded, and battery voltage is present at the "Light ON" input, then a warning chime will sound to alert an exiting driver that the lights were left ON.

"Fasten belts" warning chime
The lap/shoulder belt switch and left and right front shoulder belt switches are open if the corresponding safety belts are buckled. If the electronic time and alarm control module is grounded at either terminal C220/6 (shoulder belt input, only) or terminal C220/7 (lap/shoulder belt input), the module will sound the warning chime six (6) times and illuminate the fasten belts indicator. The fasten belts indicator
will remain illuminated until all belt switches are open, indicating that all seat belts are attached properly.

"Key in ignition" warning chime
When the key is inserted into the ignition switch, the key in ignition switch closes, applying battery voltage to pin 18 of the electronic time and alarm control module. If battery voltage is present at pin 18 and simultaneously a door is opened, grounding pin 20, the warning chime will sound, alerting the driver that the key is left in the ignition.

Ignition key light operation (if equipped)
When any door is opened, grounding pin 20 of the electronic time and alarm control module, and there is no key inserted in the ignition switch, the control module will turn ON the ignition key light. This light will remain illuminated for about 25 seconds or until the key is inserted into the ignition.