Brake indicator light on dash is on. All brake lights work when headlights are off.
Driver side brake light off when headlights are on. Have not tried new bulb yet.

 

First try all new bulbs. When changing the bulbs check the bulb socket for corrosion and if required clean it. Some bulbs are dual filament, one filament may be damaged causing the strange behavior.

 

Dual element, replaced bulb, no joy. Does each socket have a separate ground?

 

Some bulbs do, others don't.

The ground wire is white/black. Check continuity with ground using an ohm meter.

All except the high mounted bulb receive power from the same source. Have someone apply the brake while you check for battery voltage at the green/red wire.

 

Issue resolved. Ground broken at bulb socket. Re soldered to side of socket.
Thanks for all the help.

 

You are welcome. Thanks for posting back with the fix.