What causes a fuse to blow

inside the fuel tank

The question will be why is there a pressure surge in the tank. Is this pressure causing the motor to use more current causing the fuse to blow and is this a safety measure?
There may be a pressure safety valve that is dirty and not releasing the pressure or a pressure safety switch that is not cutting power to the pressure motor at a prearranged setting. Too much voltage draw on the fuse is what is blowing it.

Yes the original bad pump has damaged the drain pump circuit on the control board.

If the thermostat is not functioning properly the heater will run "wide open" and overheat.

What about your fuel rail regulator, which is in the tank with the fuel pump on some cars? Does it have a pressure switch/sensor that isn't telling the engine control module to shut the pump off when the rail pressure is obtained? If you turn the vehicle to on (not start) and the pump runs more than a couple seconds, like until the fuse blows, it could be either a stuck pump relay or worse, the fuel pump control signal. Pull the pump relay, add a new fuse and see if the pump runs with the key in the on position again, which it shouldn't. If it doesn't run, the issue is either the relay, or the control signal to the relay that is keeping the pump on all the time, causing the fuse to blow.

It sounds to me like the pressure is going to high and stalling or slowing the pump causing excessive current from the motor and blowing the fuse. If that's the case your old pump might not have been the problem. How's the fuel filter? That's in line with the fuel line to the fuel rail?

You don't have to answer the questions, just look into them for your own peace of mind.

Well code 1450 for a Ford product is a problem with the gas tank venting system.
I would think the pump in the tank is blowing the fuse, and it could be from excessive pressure in the tank.

Appears to be a short in tank circuit probably cause by a water leak in tank. These usually wear a rusty hole in the tank inside the cover and are not seen unless the thermostat covers are taken off. I would remove them and do a visual thoroughly. Anytime a fuse blows or a breaker trips is always a dead short unless you have a bad breaker. I would check those as well for vibrating, chattering noises, and/or smoking. If any of this persist, replace breaker. A melted heat element could trip them, but not usually for it leaves an open circuit instead of a shorted one.

Whats happening is the compressor is trying to start with pressure on the head/ compressor. The motor is not strong enough to over come the pressure so the motor tries to run ,may be hum a little and pops the breaker. When you bleed the pressure in the tank down the motor does not have to over come the pressure and starts up as it normally would. Now, your problem is the check valve between the tank and compressor. It needs to be replaced. It is allowing pressure in the tank back to the compressor. Thus the compressor tries to start and can't. Trace the line from the compressor to the tank. You should find the check valve screwed into the tank and the compressor discharge line screwed into the check valve. Remove the compressor discharge line,then remove the check valve. Assemble in reverse . also you can loosen the fitting at the compressor. if it blows air all the time it's the check valve for sure.

The ECM-B fuse is a 20 amp fuse, and you should NEVER put a larger fuse in to try to overcome any problem. The oil pressure switch is a secondary concern; there is an idiot light or oil pressure guage in the dash to alert you to oil pressure problems. Under heavy load, such as towing, your engine requires more fuel, and if your fuel pump is going/has gone bad, it cannot supply the demand.
The problem is almost certainly a fuel pump wire harness short, caused by a dying fuel pump. I have both had this problem myself, and repaired it on three other vehicles. On my vehicle, the wire harness had welded itself together when the fuel pump locked up, and the wire harness caught on fire.
The fuel pump is in the gas tank (of course my tank was full), and the tank has to be dropped to access it. The wire harness is modular, with plugs at both ends, and can be bought from the Chevrolet or GMC dealer.
If you put an incorrectly-rated fuse anywhere in your vehicle's electrical system, the WORST place to do it is where you have--the fuel pump circuit. Fuses blow for a reason, and the manufacturer's engineers properly size the fuses for the application at hand. Please don't do that again.
This can be a very dangerous problem and repair, and no, it is not cheap.
Do not attempt to operate this vehicle until you have had the problem properly corrected. Good luck.

dry out the area thoroughly and restart the machine to see if fuse blows with it dry - i'm not convinced this is the cause. the part you are referring to i think is the drain pump and these do lewak sometimes. the other place to look is at the door boot which if it is holed can cause water to drip down in the same area