As long as its the 5.0L 1990 Mustang GT sensor 3-wire its good.

No need to reverse the wiring until you know if its heating or not. If you reverse the wiring, you'll end up doing it again if the heater circuit is bad. So first see if it heats in its current orientation, then switch it and test.

Should save you some time.

__________________
2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k