The blue wire is the B injector drive off pin 8 on the C451 ECM connector. This fires the injector pulse.
When the ECM fires the injector, it completes the circuit to ground.
I would check for a short to ground in the harness between the ECM connector and the Injector itself.
The blue wire is connected directly to the fuel injector connector on top of the throttle body. A white wire is the 12V source from the injector fuse and ignition switch.
There is a green wire from Injector A drive on the other one, with a red wire to the injector fuse and ignition switch.
The circuit is fused on the other side of the injector, where it is connected to the power source at the white and red wires. You will have +12V at those two points on the injector connectors.
If there was a short in the blue wire to ground, then the injector would stay open all the time, which is what you described. But it would not neccessarily blow the 3A fuse due to the resistance of the injector.
It is likely that if you find no shorts in the blue wire to ground, that the transistor on the ECM that pulses the injector drive simply sorted and burned up from age. It happens. The blue wire would have gotten very hot, since this is meant to be a pulsed signal, not a constant DC voltage.
