Crank no start and fuse number thirteen keeps blowing

A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a twelve volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it is not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.

Where I would start is by removing the MFI relay, then seeing if another fuse 13 blows. If it does not, this trick will work better if you pop in a new fuse, then use the light bulb to replace the relay. Alternately, if you have my test bulb in place of the fuse, and the short is present, you should see the bulb light up for one second when you turn on the ignition switch, then it will go off. It should turn on again during cranking. Those are the two times the MFI relay turns on. That means to do any moving or unplugging of parts, you have to do that while a helper is cranking the engine. Not very practical.

Instead, if you use the bulb to bypass the relay, it will power up the circuit without even needing to turn on the ignition switch, and the bulb will limit current to a safe level. If you have the 1"-cube relays, use terminals 30 and 87. If you have the smaller relays, use the two with the arrows.

Nope. A short is an electrical issue. A wire is touching a grounded metal part or an electrical part inside the motor, in this case, is touching the metal housing.

What can happen is the fan motor develops tight bearings. That motor is not shorted, but without going into the electrical theory at this time, that will cause the motor to draw much higher current than normal. Typically a fuse for a motor circuit will be large enough to not blow during this higher start-up current. To back up for a moment, a typical fan motor might draw ten amps while it is running, but the instant it gets turned on and it is not yet up to speed, it might draw twenty amps for that one or two seconds. That is normal and acceptable. That is why when it is protected by a fuse, that has to be at least a twenty five amp fuse, to handle the start-up current without nuisance-blowing, and a little safety margin.

A lot of older vehicles used fuse link wires spliced into the wiring harness instead of regular fuses. Those were much harder to replace, but it was rare to have to do so. Those take time to burn open, just like a delayed-action fuse, so they are sized for the expected current the motor is going to draw while it is running. The higher start-up current does not last long enough to burn that link open, ... Until you have tight bearings. Then the motor runs too slowly and draws a constant current that is high enough to blow a fuse link wire.

For your story, the fan should spin freely by hand, and for multiple revolutions. If it stops as soon as you let go of it, suspect the bearings are tight.

Due to the relatively high current motors normally draw, my light bulb trick is not very effective when using a small brake light bulb. That bulb will only allow a maximum of one amp to flow. That is not enough to run the motor, but the motor is enough of a load to falsely make it look like there is a short in that circuit. When this is the case, substitute a head lamp bulb instead. A low-beam filament will allow about five amps of current to flow through the circuit. That might be enough for the engine to run as long as the fan does not turn on. If you wire in two head lamp bulbs in parallel, they will let up to ten amps flow. If the short suddenly shows up, the engine will stall, and the two bulbs will just be full, normal brightness, and the ten amps will not be high enough to damage the wiring.