You checked all the bulbs around the car or all the bulbs in the display? The warning system is for exterior bulbs.

If the warning light stays on when you turn off the lights, it means a bad turn signal or brake bulb. If it goes off, it means a bad running or headlight bulb.

It should reset when you start the engine. Do you apply the brakes when starting the engine? If you do and the light comes on immediately, it's probably a bad brake bulb.

Sixto
87 300D