Hi Mate, this is the best I can offer. Wiring says nothing about stereo being connected to the cluster
http://www.fordmods.com/ford-technic...ter-upgrade-d4
My only guess is the cluster wires are for dimming the stereo lights.
This is images of my old cluster, it's nothing great but maybe it will help.
http://oi63.tinypic.com/s5bf5y.jpg
http://oi64.tinypic.com/vbyud.jpg
http://oi67.tinypic.com/spw0hs.jpg
http://oi65.tinypic.com/dxidfq.jpg