Hi,

Any advice would be appreciated. When I press the brake, the brake light comes on. When I have the lights on, the tail light comes on. But when I have the headlights on AND press the brake, it goes dark and there is no light. This is on the LH side only, the right hand side is working as anticipated. Thanks!

 

From my memory, the brake and tail light are separate circuits except for the ground. I would first clean all the ground connections from your LH tail/brake lights.