Ok tail light info... it gets power from the 15a tail fuse. Is the fuse OK?
other than that, if you find the relay it can be replaced with a 24v relay from a generic source. No need to spend mucho dinero for a relay. But you would have to cut the wires, crimp on a ring connector to each wire and tighten on with nuts. Also the relay would have to be bolted on somehow.
Did you find the relay? It only has four wires to it. r-y x2 and G, r-b. Colours.