I have an old coleman electric furnace which is not working properly. The problem is that when the blower will quit when it is supposed to but the heating coils keep heating no matter what I do with the thermostat. I have had to cut the unit off at the breaker to stop the unit from heating. Any advice would be greatly appreciated.

Likely the relay is stuck. Follow the wires to the heating element back to a box. It should have 6 wires, 2 heavy ones in (line) and 2 heavy ones out (load). If the line and load contacts have continuity when there isn't power to the coil contacts with the smaller wires, the relay is stuck. Hitting it with a screwdriver handle might unstick it temporarily, but that would only confirm it was stuck, and should be replaced. If it is part of a circuit board, it will be tough to check and expensive to replace.