Can't get the furnace to run fan kicks in for 5 seconds then kicks out.
Only instructions are to wire the new digital thermostat using the same two wires connected to the old thermostat (mercury). No reference to colors. There are only two black wire connections coming out of the back of the new digital thermostat.

Please help. Driving me crazy!!

If you have more than 2 wires from the furnace, are there a red and a white? If so, connect them to the 2 black wires.