I would check the headlight switch FIRST. That sounds like where the problem started. Even though you don't manually "switch" it to turn the lights on and off it still is a switch (more like a relay and the day/night sensor and your ignition are turning it on and off). I have not changed out the headlight switch on these cars before so maybe someone else can chime in here about that. Also not a good idea to try a larger fuse to fix a short or overload, and that is what you have. the short will just find the next weakest link in the system to burn up. I had a friend a long time ago who bought a Chevelle. He went to put a stereo in it and found the whole fuse box (with the old glass buss fuses) was full of rolled up aluminium foil. Not a good fix.