I am hoping someone can help me out with this. I am trying to isolate a short in the wiring on an 05 STi. The fuel pump went out a couple of weeks ago. The pump was replaced but the car still didn't start. Turns out SBF #5 blew (probably when the pump died). Replaced the fuse and the car ran fine for about two weeks. Then all of the sudden SBF #5 blew again (obviously shutting the car down). Now, every time I put in a new fuse it immediately blows (once the ignition is turned on). I disconnected the fuel pump and relay and the fuse still blows. The only time it does not blow is when I disconnect the main relay. I have also tried disconnecting the o2 sensors (both front and rear) but they have no effect. Obviously this leads me to believe that the short is either in the main relay itself or with an associated component. The problem is that I don't know what the main relay controls. Any ideas would be greatly appreciated.

change the main relay .

Ok, I swapped the main relay with one from my 03 WRX. Now, the fuse does not blow but the main relay makes a loud buzzing sound, the fuel pump does not prime, and the gages don't work (the gages were working before). Any thoughts?

anyone???

The short problem is still there. The relay isn't the problem, like you suspected, the problem is on the circuit the relay ties to. Here is a list of places that SB-5 ties to

Data link connector
Engine control module
Fuel pump relay
Main relay

If you can locate these you can try isolating them and then connect the main relay up again and see if it works without buzzing or blowing a fuse. Then connect up one circuit at a time. The faulty one will cause trouble again whenyou try to connect it. Using an ohmmeter would be a big help here.

Cougar4
Thanks for the advice. I have made a little progress. Here are the notes that I have been keeping throughout this process. Let me know if this brings up any more ideas.
1. SBF #5 blows as soon as ignition is turned on. (Items associated with SBF #5 Main relay, OBD port, ECU, Fuel Pump relay, O2 Sensors).
2. Disconnected fuel pump and relay. (no change)
3. Disconnected o2 sensors front and rear (no change)
4. Checked all engine harness wiring for any damage/shorting. Checked all under vehicle wiring including transmission, rear emissions components, and rear diff electrical connections. No damage found. The only minor wiring issue found was that one of the electrical connectors (mounted on the trans and close to the turbo) had the plastic loom melted off. The wires were intact (note: this connector was disconnected for the remainder of the testing).
5. Disconnected main relay, SBF #5 no longer blows
6. Replaced main relay with a known working relay and reconnected. (SBF#5 remains working when ignition is turned on). Note: main relay makes a loud “buzzing” sound.
7. Reconnected fuel pump relay and fuel pump, SBF#5 remains working however fuel pump does not prime.
8. Noticed “feedback” sound coming from speakers when ignition is turned on.
9. Disconnected all aftermarket stereo equipment. (no change)
10. Removed radio, found loose wire in radio wiring harness grounding to the bottom of the radio. (red wire with white stripe)
11. With radio wiring disconnected and loose wire repaired (note: no other changes have been made from above description) SBF#5 blows. Definite electrical odor. This has not occurred at any other time. Obviously “feedback” sound no longer occurs.
12. Disconnected fuel pump and relay (no change)
13. Disconnected Main relay, SBF #5 no longer blows.
14. Reconnected radio and reinstalled. SBF#5 remains intact. “Feedback” sound returns.
15. Attempted to scan the computer for codes via the diagnostic port. Made multiple attempts. Code scanner was unable to communicate. (link error). Note: this may be attributed to the reflash software (ECUTEK- relfash) but not likely.

Very good job on the notes. You have a good logical troubleshooting process.

I have to wonder now if the short is in the ECU. I hate to say that, try disconnecting it and see if the main relay acts normal then. The reason the relay is doing that is because the supply voltage is flucuating as the relay closes. There now may be a problem in the wire connection between the fuse and the relay causing this to happen since the fuse is no longer blowing out. When the relay closes and supplies voltage to the load, the voltage drops due to the high load it turns on (or drops due to a problem with the source connection). The low voltage causes the relay to open and so the supply voltage then goes back up when the load is disconnected, turning on the relay again, this process goes back and forth.