Ok what I have is a Carrier {edge}. Removing it to install a Filtrete 3M30. I have two wires coming from the wall. One white & one red. The back plate to the Carrier has a 4-wire hook-up. From the wall wires red go's to V White go's to Vg Then there are two wires coming from the back of the circute board from the Carrier to the same back plate one red the other black. Red go's to V black go's to Vg Confused yet? Well now you know where I am coming from. My furnace is elictric but has back up oil & we also have AC. So any help would be appriciated believe me! The Filtrete customer service dept. Must be out to lunch or maybe they just don't want to answer there phones! Thanks for any help offered! Brian.