I have a Honda Civic 2-door 1994 which does not sound when I leave the car with the lights on. This applies both the cabin-lights and the headlights. Is there any easy way I could fix this? Is it a fuse or a sensor which is malfunctioning. Btw. The car sounds when I leave the car with the key in the ignition.

I don't think there is such a thing as lights-are-on alarm signal in a Civic. I'm sure there's no such thing in a '91 and before Civics. But there are these little Piezzo Speakers that you can buy (as a kit) for a buck or two, which you can connect to the fuse box (probably to "lights" and "power-when-car-is-on" connectors) which will produce a sound once you turn the car off and have the lights on.