I recently purchased a WIFI thermostat that requires the use of the "C" terminal. I do have an extra wire available to use on the C terminal that runs from the wall unit to the furnace. However, there is no terminal board/block at the furnace. The thermostat wires connect directly to the furnace wires and inside the unit, there is no terminal block. This is an old GE unit and works fine. I just need to know where I can connect the "c" wire at the furnace.