We're at the point now where any further input would be guesses. We need to know the resistance across the two wires coming from the rear sensor. Can you trace them to where they enter another harness and get this reading? It should be about 100 ohms. If it's a lot less than this, there's a short somewhere. If it's a lot more, there's either an issue with the connector/harness, or the sensor is not making a good ground contact.