There is a very good chance an animal has bitten your wires and somewhere along the line there are probably 2 wires touching metal to metal. If you can I would find a schematic and follow the harness but it is most likely under the dash. I had a very similar problem on a 94 mustang GT but eventually gave up and sold it as is. My speedo was not working either. But now that I am older and wiser I think I could have fixed it.