Could just be that one of the switches is a bit worn and isn't going down as far as it should.
Close all doors and the boot and check the light stays on.
Open a door and find the switch - a kind of plunger - and push it in and out several times to the maximum it will go. If the light stays on constantly, then close that door and try the next.
The boot is probably included as well, sometimes there's a different light for it though.
If you do find it, a couple of strips of tape on the door where it strikes it should work.