Well, we moved into this mobile home about 3 weeks ago. We have our a/c and oil heat connected to one thermostat. It was all working fine up until a few days ago. All of a sudden, the heat would not shut off at all. Eventually it got up to 90 degrees in here and I just opened the door to the furnace or whatever and just unplugged the motor. After a few minutes it went off. But when I plug it back in, it starts right back up, even though it is turned off on the thermostat. The only time it will stop running is when its unplugged. The a/c works fine I can turn that on and off with the thermostat... but the heat is all messed up. I can actually have both the heat and a/c running at the same time now as long as the heater motor is plugged in and the a/c is turned on with the thermostat. Obviously, there is a huge problem here... someone please help me because we can't really pay someone to come deal with it right now

Either the red and white wires from the stat to the furnace are pinched someplace, causing a short , or the stat is defective. Take these two wires off the stat, if the heat continues, the wires are shorted, if not, replace the stat.

Either the red and white wires from the stat to the furnace are pinched someplace, causing a short , or the stat is defective. Take these two wires off the stat, if the heat continues, the wires are shorted, if not, replace the stat.

There is 2 sets of red and white wires...

Then work with the pair that should take care of the heat, usually R and W terminals on the stat

OK I disconnected them, and the heat still runs. I think I would have rather just replaced the thermostat. Considering the wires are running either above the ceiling, or in the walls somewhere, how am I supposed to check for a short?

Since you have disconnected the stat, and the heat is still running, you probably have a short in the wiring, anywhere fromn the stat to the furnace.

Or a relay is stuck in the furnace.

To check for a short, you need to trace the entire length of the cable looking for a something pinching the cable, or a nail or screw driven through the cable.

May be easier to just run new cable.