Re: Tail light issues...
Yes those two circuits should be on different fuses. However if the tail light on the other side is working, then the fuse is not the problem. Are you sure you are using the correct bulb number? My next test would be to see if voltage is present at the socket with a 12v test light. It is possible you have a defective socket at that light. I replace headlight and taillight sockets weekly on our Ford vehicles in our fleet at work due to the sockets melting and causing a bad connection to the bulb.
James