Classic symptom of a broken ground wire on the right rear. If you remove the left rear brake light bulb, you will see the right rear one no longer works. Or, if you watch closely, you will see the right rear brake light is not as bright as the left one. With a broken ground wire, current for the right rear brake light cannot find a path to ground, but it finds an alternative path by doubling back through the tail light filament, then over to the left tail light that is connected to it, then to ground on the left side. Since the 12 volts is being split by three filaments, each one will be rather dim. What you are seeing on the right side is the brake light and the tail light both on at one-third or less normal brightness.
An additional clue is the symptoms will be different when the tail lights / head lights are turned on.
The signal light on the dash is on because it is tied to the right signal / brake lights. I suspect you have two bulbs in each rear corner. One is for the brake light and one is the turn signal, but both have a tail light filament in them too. That is why they interact when the ground wire is broken.
Sunday, July 24th, 2016 AT 11:20 PM