The 5 amp fuse on my AC/Heater control board blows when I put the setting to heat
On the furnace control board again jumper the red to the white.  Everything OK?  Now, on the new stat wire, disconnect the Stat completely.  Now at the stat location twist together the red and the white. Does the fuse now hold.  The furnace should start.  If this is the case, you are doing something wrong when you are connecting the stat. Happy hunting and Good Luck.