Audio Systems: Light Bulb Issue, mercury switch, cadillac deville

Question
I know that my question has nothing to do with stereo system but being that it is an electrical issue, thought you could help Thanks!!
>>>>>>>>>>>>
Hi, I just bought a 1986 Cadillac Deville Sedan. Under the engine hood is a assesory light. At first, the bulb didn't work now it does because I replaced it! Problem is......The light only will come on when the engine is turned on and the headlights are on. Doesn't seem odd?
I thought that this light would work like the lights that come on when you open the car door. Were the engine dosen't have to be on. Just the fact that you opened the hood!
Please explain to me if you think this is wrong or not. I thought that just simply opening up the engine hood, that the light would just come on without the engine being on, et.
Hope you understand my issue here. Thanks!!
Tom

Answer
you are wrong, the engine don't need to be on.
The key needs to be in the accesorie possition  also the headlights don't need to be on only the parking lights  

will you open the hood on the midle of the night and have  the parking lights off ? safety
if is day time do you needtouse thelight inside the hood ?
some have a mercury switch behind the light  connector