Help: Headlights Partially Working

Any tips or ideas are greatly appreciated... I have a 1992 Ford Explorer, 4-door. Recently, I drove into a campground late at night, turning my headlights on and off, so as not to disturb the sleepers. Early the next morning, I discovered that my headlights didn't illuminate by pulling the switch. Furthermore, the highbeams didn't work when I move the highbeam (turn signal) switch into the position that locks the highbeams on. BUT, when I pull back on the highbeam switch (to illuminate the highbeams only temporarily with the spring-loaded switch), the highbeams DO work! What happened? Which components are suspect? How do I test? I did check the headlight fuse under the hood (and it sparked when I put the fuse back in, with the engine off and the lights off, hmmm?). Sheffel ... at ... usa ... dot ... net