From what I recall it simply limits the hold current for the injector, its bypassed during the initial injector opening phase to achieve the peak current.

 

Yep. For a fast opening and closing injector, you can use plenty of current and a low inductance injector, but you need to limit the current once it has built up far enough to hold the injector open or it melts. A ballast resistor is cheap and reliable solution.

The ECU supplies 12v to the injectors through the resistors for the full duration of the injector pulse. The initial short duration "OPEN" spike is sent on separate wiring directly to the injectors without passing through the resistor pack.

At idle you can disconnect the resistor pack completely and the car will continue to idle. I'm not suggesting it, when I accidentally did the adrenaline rush was surprising. It was fine. The initial "open spike" is apparently sufficient for idle fuel requirements.

 

The ECU is wired in Peak and Hold with outputs for Peak and separate outputs for hold which go through the resistor pack.

The injectors in the V12 are about 1.6ohms (R) each and are wired in parallel in bundles of 3 so the resistance is actually 0.53ohms and the current the ECU has to supply is 22.6amps now if the ECU had to supply this current for the time injectors were needed to be open then the heat generated would be significant.

The resistor pack is a current limiting device designed to limit current I=E/R