'84 Alfetta Q.O. - Check Control malfunction

[Q.V.]

Not sure many of you dealt with european vehicles, but...

Check control lightens position and brake lights' warning LEDs when the lights are on (they all function as must do!), but doesn't lighten them when connectors or lamps from both sides are taken off - did anyone of you faced this kind of problem?

ARC panel looks like this:


I failed to find any info on this device - diagrams or revival suggestions - there are only about 75/Milano ARC. Will be grateful if you help to find some