3rd brake light on Buick Roadmaster not working?

If the third brake light on your Buick Roadmaster is not working, first check the bulb to ensure it's not burnt out. If the bulb is functioning, inspect the wiring and connections for any damage or corrosion. Additionally, verify that the brake light fuse is intact and check the brake switch to ensure it's operating properly. If these components are all in good condition, it may require further diagnosis by a professional.