my truck had the same problem but when I turned my blinker on both brake lights lit up. The next day I checked for a ground issue and that fixed the issue.
Over the last few months my heater will throw a fit when I start my truck, and lately as it has been getting colder it flickers and flashes more rapidly than usual. I have checked the connection and cleaned the connectors but no luck. I would buy a new unit but have no idea if that is the actual...