Your turn signal switch is faulty. It'll keep on being faulty whether or not you eventually come to understand how it works (and why it doesn't). There are separate power paths within the switch for _each_ turn signal (left front, left rear; right front, right rear). There have to be, because otherwise the front turn signals would both light up solid whenever you step on the brake. Again, power for the stop lights goes through the turn signal switch, and the two wires that run from the turn signal switch to the rear lamps carry steady voltage for the stop light function and pulsed voltage for the turn signal function to the same filament in the same bulb on each side.
(But maybe if you ask the question a couple dozen more times, the answer will change, though, LOL.)
That'd be telling. Keep thinking about it. The answer's right here in this post.
