The Fan won't shut off. It drained the battery

I have seen this on another car line, if the radio shuts down electronically and it can glitch thereby not shutting everything off. The fix was a software change by the radio manufacturer. Check if others are having the problem, I am not familiar with your vehical.

You mean with the engine running? If the engine is running, the heater fan should be getting power from the alternator, not the battery. Does your battery light go off after engine is running? Or does the voltage gauge show normal charging when running?
If you can start the truck, have your charging system checked out. If it won't start now, have the battery charged up and try again. Then have the charging system checked. If it is good, your heater fan may have a short and drawing too much current, But a heater fan will run the battery down pretty quick, if the engine is not running.

Find & remove the fuse or relay

That suggests that the problem is in the harness, something in the connector or wiring is causing an open circuit. You will need to have the circuit tested to find the fault. Ford alternators have known connector issues & new aftermarket connectors are readily available at most auto parts stores.

I suspect parasitic draw. All vehicles draw some power from the batteries when the car is shut off. Certain accessories such as clocks, radios remote door openers and alarms always need power. The normal power used is called parasitic draw.

It is always a very low draw so it doesn't run the battery down. If you install accessories like shortwave radios or plug things like inverters and portable refrigerators into the accessory socket and operate them too long without the engine running you can drain your batteries to the point where the engine won't start. If there is an electrical short in the vehicle or a malfunctioning accessory it could be drawing much more than its normal load causing a drain on the batteries. If you leave your door open and the inside lights stay on all night you could drain the battery down till the car won't start.

Here's also a good resource for your car specifically on narrowing down the cause of the drain.

Where did he get the power from to run the fan,if he just used a hot wire from inside the car it most likely blew the fuse for ignition as the engine fan gets its power from a relay in the power distribution box under the hood as far as the fan goes if it ran with the wire then the engine coolant temp sensor is probably bad

Try lubricating the door latch in the door. You can also use a screwdriver to see if you can get the mechanism to move freely.

It drains battery while car is off? If so, hook up a test light. Take negative cable off and put testlight between cable end and battery post-is light on? Then there is a drain. Go to fusebox on driver's side of dash and begin removing fuses till light goes off-that is the circuit with the drain. Identify the circuit and repair the problem.
That 40 amp fuse would be a main supply feed to several circuits, I think. Sometimes the problem is a trunk or glovebox light that won't go out as supposed to.
Good luck.

Has it been recently fitted? Most stereos require a permanent 12 volt supply and a secondary one connected to the ignition. Perhaps these have been mixed around causing the stereo to remain on?

you might check your switch sounds like to me that your two lower speed sides of the switch maybe burnwed out.