6 disc indash changer, not lighting up

[suzucati]

Have fitted an indash changer to my megane cc 2007, all works fine but just
cant find out why it doesnt illuminate with the rest of the dash, have found
a small black plug in the loom, same shape etc, but still nothing, thinking
there may be a fault in the loom, as i have tried two changers and neither
light up.
Have found a small black plug in the loom which matches the plug shape on the back of the changer, plugged it in but still nothing, took a voltage reading, but found no output from the black plug, need to trace were this plug goes, as i thing thats were the problem is.
Any help would be great.