Anybody know how to troubleshoot a dawn-to-dusk security light? It's American Electric model #R-175M, with a 175w metal halide clear bulb. I replaced the bulb but the fixture still doesn't work. Perhaps the photosensor or ballast have given up the ghost, but I don't know how to test these components. The fixture is about 20 years old. Guess I should be happy it has lasted this long, but I don't want to replace it if I can repair it fairly easily. Any electricians out there? Thanks.