Hello.
If the brake light switch is bad the taillights will still come on when you turn on the headlights.You can eliminate or confirm the brake light switch as the problem by unpluging the little two-wire connector from the switch, take a paperclip and bend it around so that you can stick the two ends of the paperclip into the holes of the connector.The brake lights should come on when you do that. Don't use this test procedure to check for problems in wall outlets of your home.
If what you have is the turn signals work, but the taillights don't come on, the headlights do come on and the brake lights don't work, then your problem is either those astonishingly poorly crafted Scott Drake taillight buckets or the connector that plugs into the back of them. If the taillights don't come on when you turn on the headlights, try turning on the headlights and twist the connector around some on the back of the tailight bucket. If they try to come on that's your problem.If the tailights are coming on now when you turn the headlights on take a stick or a piece of a 2X4 or something and stick it between the brake pedal and the front of the seat to simulate someone pushing on the brake pedal with their foot, being careful not to damage the upholstery, and go wiggle the connector on one of the taillights around. Hope that helps.
brake lights on a 1966 mustang 
