My interior light and the back-up lights are on the same fuse and the fuse keeps blowing each time I change the fuse. Scratching my head on this one...

 

You obviously have a short in one of the circuits. I would first check the back up lights since they are exposed to the weather. Check the bulb sockets and the wires going to them for shorts. If that doesn't help then do the same for all of the interior lights.