A Nissan wiring diagram is truly impossible to read. A few things to check are the QGS/other fuse, the ignition diode that is located inside the frame located behind the lower relay box. Some were a chocolate brown color or could be yellow in color and attached to the main wiring harness. One of our customers found a wire in a harness that rubbed through against the fuel rail and was shorting out. Your plugs on the coils should have a ground, battery voltage, and 2 volts while cranking the engine over on the signal wire then it drops to 1 volt while running. I would also use an analog type voltage meter to test it if you have one available. Check these out and hopefully you can locate the problem.