Use a voltmeter, set to test resistance (impedence). Put a wire on the pin of the engine harness that you want to test (so you can get inside the car with the voltmeter), and with the ECU connector unplugged, probe the pin on it designated by that wiring diagram and see if the voltmeter moves. If it doesn't move, there's no continuity. If it does, you're fine. Test all the wires you can.

If that doesn't make sense to you, find some old guy somewhere that knows electricity, and ask him how to test continuity. He might be able to explain it better than me.