headlights

I had a rusted out 1978 3/4 ton 4x4 with a new motor and trans. Had a 1982 Blazer with no motor and no trans. Switched everything out- but I'm having problems with the headlights. If the parking lights are on, fine. If you turn the headlights on it blows the fuse and you have no lights. Obviously a short somewhere, anybody know an easy way to find it? Or any other suggestions?