Thanks for your reply.
Yes, I replaced the fuse and it blew again. With the correct fuse and new main relay installed is when the CEL flashed and the fan cycled.
I haven’t tried to read codes since SBF 5 is the battery or constant power supply to the ECM. As stated, the fuse blows almost instantly so I don’t want to damage the ECM. For test purposes I am using a 30 amp circuit breaker in the place of the fuse.
I have unplugged everything in the direct power supply from SBF 5. I have also unplugged the harness to the fuel pump after testing it for functionality, and unplugged all sensors and components powered by the affected side of the main relay.
I agree with you that there is a wiring issue somewhere, just a matter of finding it. I will check out the CAN bus communication and 5V ref that the rest of the sensors are on.