Why don't my brake lights work when I turn on the headlights

Last one I inspected was circuit boards in the rear lights. It was a 91, You must use a schematic and verify fuses, grounds and presence of components in the schematic and be sure you read the right schematic for that year and model and options. after many trips for correct info, I found some components werent actually there, other parts for other systems were in that place, and Napa has the ability to get the parts you might need after diagnosis is complete

You have to be pressing on the brake pedal to get the brake lights to work. Otherwise, they are your running lights.