whats gone wrong?

Is this the fusible link on the earth lead at the front seat?Have you been trying to tow/bump start the motor?These are designed to fuse in these situations and think it is to prevent a voltage spike blowing up ecu`s.I would first remove the fuel filter and check for water ingress,check piping also for chaffing and a code reader may be worth looking at also to see what faults are stored.

cdc
June 2013