Could you possibly have damaged the harness, or did the heat shield ever come in contact with the altertator? If you touched the alternator with the heat shield, then it could have blown out your sensor. There would have been sparks if that happened and you'd know it.

Inspect the harness and plug to make sure everything's kosher. It's a little weird for the heater circuit to go bad after removing a heat shield. Were there any ground straps on the heat shield?