With the ignition on, you should see battery voltage (12.4 or whatever) at all points of the injector wiring as long as the injector is not on. You'll have 12.4V at the ballast resistor input, same at the output, same at both sides of the injector connector. With no current flowing, all points should be at 12.4 volts. It is only when the ECU grounds one side of the injector that you'll get current flowing and voltage drops.

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