Starter Relay fuse blew...replaced and immediately blew again.

I don't have my wiring diagram handy at work, but I think the 20A fuse that popped protects the solenoid that pushes the pinion gear forward to mesh with the flywheel ring gear. It does not protect the starter relay.

What this means is that the problem is probably not the relay (though it is remotely possible), but either a short to chassis in the wire to the starter motor, or a bad winding in the starter. I would check the small wires to the starter and the resistance of the solenoid before buying a new relay. A 1 ohm solenoid resistance equates to a ~12 amp current, which is less than the 20A fuse rating. Any resistance well under 1 ohm would be suspicious. The resistance can be measured at the relay socket between the contact terminals and ground. Disconnect the battery negative cable before making any measurements.

OK, I got my wiring diagrams. They are for '03, but I expect '04 should be identical. Forget most of what I wrote above; it is probably wrong .

There are 2 fuses that protect the starting system. One is located near the battery, and the other on the underside of the instrument panel.

The fuse near the battery is labeled "starter relay & ignition" and is supposed to be 40A. If that's the fuse that is blowing, my previous message applies.

The fuse under the I/P is supposed to be 20A, and labeled "starter relay & radio". It protects the circuit that powers the relay coil. A red / blue stripe wire runs from the fuse to the clutch switch (manual transmission) and park/neutral switch (automatic transmission). From there, a white / pink stripe wire runs to the starter relay coil.

I have seen a previous message on Stangnet where one of the pedal arms chafed a wire and caused a short, so that is the first place I would look. A/T cars have a jumper in place of the clutch switch, and M/T cars have a jumper in place of the transmission park/neutral switch.

While a shorted relay coil is a possibility, this to me would be rare. You can remove the relay and check the coil resistance with an ohmmeter. It should be no less than 25 ohms.

Also, does the fuse blow with the starter relay removed? If yes, that eliminates the relay as a cause - don't bother to buy a new one.