You did not switch the sending units for the water and
oil temp did you? I think you can take the gauge out and test it with hot water and a 12V power source. Also you can check the gauge by grounding the wire to the block and see if it pegs out to the hot side of the gague.
Is your motor properly grounded to the chassis and the gauges need to be grounded to the chassis or engine.
No ground strap on the motor can cause many problems