2005 Ford Focus blows 20 amp #9 fuse

If fuse blows instantly, then there is a short to ground in circuit.

If it runs for a while then blows, there is high resistance in the circuit, intermittent short to ground, or surge in power.

The only thing you can do is follow circuit, looking for any breeches in wiring protectors, burn marks on wires, or wires that have come loos from brackets and are near a high heat source (exhaust).

Otherwise you would be better off going to shop and have the electrical system scanned to isolate problem.