I haven't had to deal with a headlight issue with my 71 Cutlass for decades, so I guess I am due. I got home tonight and noticed my passenger low beam (outside light) is not working. The driver's side is. When I put the high beams on, all 4 work. Is this a wiring issue or is the bulb outside bulb needing to be replaced?

 

The low beams are dual filament, so it's possible to have the low burned out and the high still working.

 

Change the lamp, I like to do it in pairs.

 

When you change the lamp make sure you clean the wire terminals with electrical parts cleaner and a soft bristle brush.