I have finally fixed the alternator problem, and it was not really straight forward;

After knowing about the relay and the red light in the 24 volt panel, I soon discovered that the circuit for exiting the 24 V alternator and lighting up the red light was not correctly installed.

There was one wire connected to the + terminal of the alternator, this small gauge wire was moved to the "F" terminal of the alternator, and now the red light works as expected (lights up when ignition "ON" and turns off when motor starts and alternator delivers power).

Thank you for all the input, your help was crucial for me finding the fault and correcting the problem!

BR Niels