If I understand what you are saying, you might have it wrong... according to the manual, the white wire you want comes out of the gauge, so you should not have to 'tap' the wire anywhere. If you hooked in between the sensor and the gauge, that is incorrect. The wires that go to the sensor are either heater wires or unconditioned / unscaled raw output from the sensor. The gauge typically contains the controller that runs the heater for the sensor, and reads in the raw voltage from the sensor and displays it and converts it to 0-5v and serial stream. On the 4 pin connector on the back of the gauge, a white wire should come out. Hook that to the MS Ecu directly. If you hooked into the sensor white wire, I'm not sure what it does, but that would explain your high voltage reading on it. I'm not sure how protected that input is on the MS ECU, so you might have toasted it. Not that big of a deal probably if it is toasted, because there should be a spare analog in you can use (maybe), or you could toss on a canbus module if it is hosed to get some more inputs.