...BTW your Bieber avatar is awesome.-Malone
I have no clue on electric stuff in these cars. That being said the only thing that I could for see is the new cluster is bad. Try just putting power to the lights to see if they work.
Finally got my bentley back.. Lemme see if I can help at all...(Rambling out loud)From the head light switch there is the gy/bl wire which you had mentioned.. That is the one that powers all the instrument panel lights.. Ashtray, cluster, radio, AND the flasher switch.. From the head light switch it leads to a 4 amp fuse (#5 in the panel) From the fuse panel (still a gy/bl wire) it branches out to all the dash lights.. For the cluster it leads to the #6 terminal in the plug.. The lights in the cluster ground though pin 5 (black or brown wire)Does your ashtray or hazard switch light up?