brake lights......

its a 1970 camaro. with everything off, i push the brake and the right brake light illuminates and the left one lights up too. but, the left one is alot dimmer and is as bright as a tail light. (so im kind of thinking that the tail light just comes one, not the brake light) if i turn the tail lights on, and then push the brake, the right light brightens (brake light comes on) and the left light goes completely out. the is no light at all on the left when i do this. i really have no clue as to what the problem is.