1990 Mercedes Benz SL500 Rear High Mount Tail Lights

I would check all your fuses to begin. If all look good then check the rest of your brake lights. If you see no brake lights you may have a failed stop lamp switch. If the brake lights work but the third brake light is still inop check the third brake light connector. These sometimes get a small water leak and water will travel down the wires to the connector and corrode it. If this is the case it will be necessary to replace the connector as well.