I recently replaced the battery in my 89 Ranger and foolishly did not tighten the negative connector enough. It came loose while driving which was easy enough to fix. However during that process one of my headlights stopped working. I imagine it shorted out from the loose connection but I'm not sure. Would you start with replacing the fuse or bulb?

 

Welcome to the forum

Battery is not used at all when engine is running, alternator provides all vehicle power, so most likely the bulb burned out
I don't think 1989 had each bulb on its own fuse, so just check/replace the bulb, give wires a good look


A car Battery is 12.3volt to 12.8volts
Working Alternators minimum voltage is 13.5volts
So when engine is running voltage flows TO the battery to keep it charged up
And all electrics in the vehicle run from alternator voltage

Many people tested if an alternator was working by disconnecting battery's negative cable while engine was running, if engine stalled then alternator was NOT working, if engine kept running then it was working
But not a good test to do with today's computer operated vehicles, lol
Better, and easier, to just use a Volt Meter