to make work a searshlight you have to do that!
1. put an AI antiaircraft object (not sure of name i play in frensh) and define an radius (100m per exemple)
2. in the properties of the AI objeect choose start up.CPP
3. put a generator inside the radius of AI object (static ---> environnement ---> generator)
4. link the AI object to the generator by the button set to... (you will see a yellow line linking the generator and the AI object.
5. put a searchlight near the generator. (don't forget to put the generator and searchlight in the radius of AI object)
it is done... now when a plane fly in the area the searschlight will work. and if the generator is destroy...the search light will stop working.
one more thing... apparently there are more powerfull generator an less powerfull one.. IMO you can put severall searchlight to one generator. but if the generator is not full enough it can't make work all the searshlight.