the blue with yellow goes back to the ASD relay then on to the ECM.
If this is the case it is the ground to the coil side of the asd relay. The ECM will supply the ground for the asd to come on(ignition on no crank) but go off in a few seconds. It sounds like the ecm is not supplying the ground for the relay to come on.
You need to check this with a meter! Put one lead on the positive battery terminal and the other on the blue/yellow wire lead. As soon as you turn the ignition to on you should see battery voltage.
I get what you are trying to tell him but he should get 12volts from A of the asd, to ground, key on, and able to pass a load test. The blue and yellow must also be able to pass a load test , a meter is not good enough. If both of those will pass the load test, and it runs with that relay jumpered it should be the ecm.
Looking at the diagram if it runs with pin B and D jumpered, or D grounded, it almost has to be blue and yellow wire from pin C to 51, or the ecm.
