2005 Subaru Legacy 2.5XT turbo

Initial problem: rough idle, check engine light on, P0304 code.

Replaced all 4 plugs and the coil pack on #4 cylinder. Cleared P0304, performed idle relearn and drove the car two weeks. Check engine light returned as well as P0304.

Put a spark plug tester between the plug and coil pack on cylinder 4 and stared the car. The spark plug tester was flashing and looked ok. 

Here’s where the problem started. I replaced the connector (a soldered splice) with one from the junk yard because I broke the original earlier. I didn’t disconnect the battery before splicing. I didn’t try to start the car here.

For comparison, I put the spark plug tester on cylinder 3 (a known good cylinder) and tried to start the car. No crank, no sounds from the starter or fuel pump prime. All other electrical, dash lights, windows, radio, etc working. Removed the spark plug tester and still no start. Scanned for new codes and got “error”.

Checked the battery voltage (1 year old), 13 volts. 

Broke the positive battery terminal when trying to clean the terminals. Replaced the broken terminal 3 days later meanwhile the battery was left disconnected. Checked the voltage at the starter, 13 volts. Checked for 12 volts at the solenoid with the key on, nothing.

Checked fuses,

#5, engine bay

#13, engine bay, ECU

#11, engine bay, fuel pump relay 

#21, main cabin, starter relay

#13 main cabin 

All ok.

Removed and inspected ECU for signs of damage, no burnt or discolored components on board.

Did not check clutch switch or any relays.

Thinking that the fuel pump relay is shorted because fuse#11 main cabin blows when the key is switched to on. Removed ECU and rechecked fuse#11, still blows when key is on.