Search the Internet for your thermostat and you will see how to wire it correctly to the furnace. However I suspect it won't run the heat correctly and that's why your friend hard-wired the system. So once you have the thermostat wired correctly, tell us what happens.
Usually the control wires from the thermostat to the furnace are colored to correspond to the terminal letters... red wire to the R terminal on the thermostat and at the furnace, green wire to the G terminal and so forth. Make sure there are no splices to the red wire at the 'stat is the same wire(red) at the furnace.