I am unsure how it is wired but there is a signal to and from the ECU.
So I believe the ECU controls it in a way.
However as mentioned I swapped ECUs thinking that might be the issue and it behaved exactly the same.
I was looking over some Mitsubishi diagrams, I used a 2003 Diamante for the example......
It appears the the ECM just monitors the "Lamp/Turn-on" for incorrect voltages (High/Low) & sends a data signal to the gauge cluster if a fault is present. The Cluster uses a transistor to control the Charging Lamp
The Generator Relay Coil is what passes a resisted ignition hot turn-on signal to the regulator.