So the S5 has a larger water temp plug comapred to the s4, can I just attach my S4 wire to the to the S5 sensor to have it work for my gauge?

 

Yes. As long as the wire in the harness that you are using is attached to the sensor, that's all that matters. Whether you need to wire a new connector to that particular coolant temperature gauge wire or not, it needs to be attached to give a reading.