Hi mate,

There will be two wires from the ecu to the multiplug on the injector loom, the injector loom then has four wires going to the injectors.

1&4 are joined
2&3 are joined

each plug should have 12v on one pin when the ignition is on, the other pin should buzz through to the joined injector connector....

So 2&3 will buzz through, as will 1&4 if the wiring is fine.

My money is bang on a broken wire, mine did the same.