Hi,
Turn your key switch to the on position and see whether only controller's green light illuminates.
Then turn off the start key and disconnect sw as well and disconnect the connector near the monitor panel.
Now turn on both keys and check the voltage between number 5(green wire) & number 2(black wire) at the female side of the connector.(numbers should be marked inside the connector) and the reading should be 3.0v to 4.6v .(dc)
Now check the voltage between number 6(brown wire) & number 2(black wire) and the reading should be 0.1v to 1.2v .(dc)
If these voltage levels are not with in the limits either your controller or wiring is defective.
So you can check the above mentioned 3 wires by refering schematic to determine that the wiring is good or bad ( black wire is the ground wire, green wire is the cat data link + wire, brown wire is the cat data link - wire). Do a continuity test, ground short test, B+ short test on these wires.
If the wiring is ok that means your controller is defective. That means there is a communication signal error.
If that has happened, if you have an oscilloscope then you can check the wave form of the data link signal and it should be a clean pwm signal if working correctly. But if the signal is corrupted then you can see that what has happened to it. And that information is vital for a good electronic technitian who is familier with micro controller units, if you planing to repair the controller.
