Visited by the electrical gremlin

[cali_surfer]

I need some help everyone. I just got done doing some work on my truck.... replaced the alternator, change oil, change tranny filter/gasket. For some reason, the headlights don't work now. Let me explain. I got all my mechanical stuff done, test the alt to make sure its charging by putting a full load on it--turn on all accessories including lights, a/c, radio, etc. Everything worked great, alt was putting out right voltage, so I was happy. Left the truck at my buddy's shop (where I was working on it) overnight. So today I go out to get it and I pull the headlight switch to park lights, they work, but then when I pull to headlights the park lights go off but headlights are on. I scratched my head and shut the switch off. I pulled it in and out a couple more times and had similar luck, then it blew the headlight fuse. Oh, I might add I have a Painless wiring harness. I bought a new switch, installed it, same problem. While working on it I hit the horn button (grant steering wheel) and that didn't work either. What gives? Everything else works though, my brake lights light up when the peddle is pushed and the turn lights flash when activating the turn switch. I didn't touch the electrical system when doing my work, weird coincidence!! Any help would be appreciated.