91 s10 Headlights

my headlights won't come on but everything else works like parking lights and blinkers

My headlights started doing that. Or maybe it was just the left one. I noticed a wire going from left one to horn mount. Upon cleaning and tightening the wire connection at horn mount, headlight was fine. Ground wire I guess ? Or maybe your plug connections are lose or dirty ? Or the little relay box (under hood at firewall ?) has problem ?