1992 Oldsmobile 88 Break lights

Hi, does the left turn signal work, at the rear, with headlamps on? The reason I asked, that is a dual filament bulb. One filament for stop/turn, they don't use the circuit at the same time. The other filament, is for tail light, goes hot when you turn on the head lamp switch. Brown wire is voltage for tail lamp-- yellow wire is voltage for stop or turn-- black wire is ground.

All of other functions work in the tail lights on both sides. The running lights work but disingague once the break pedal is pressed, but no break light. I had someone sugest the switch under the dash that recognizes when the breaks are depressed, but it seems to be functioning fine.

About all I could do is backtrack the circuit when the problem occurs. You could use a testlite on the brake lite wire, for voltage, when it refuses to work. I gave you the wiring color. If no voltage, backtrack the circuit.