My 3 units could be considered overkill but any FSD issues are short lived by simply unplugging the dummy plug from spare, and active plug from failed unit then switching them. Had to do this once when my IP was failing the unit I switched to had a #9 resistor that kept my truck running until I had replaced IP (mechanical cam ring failure).

My first thought was the FSD w/#5 resistor was bad "it wasn't". Bill Heath pointed out that the #9 had enough extra fuel to run motor and the IP would have to be replaced soon "he was right".