I've had instrument cluster problems before on other cars but this one's got me stumped. '88 740, no cluster/dash lights, tried bypassing the dimmer (connected red&blue wires on back of rheostat at cluster, right?), have power at fuse 10 when the headlights are on, nothing funky looking in the flex circuit. It didn't have a radio in it when I bought it, hooked up a factory radio (matched the wire colors), no lights either way. There is a large gauge black wire that's still loose, figured it was for the cig lighter but not sure. Tried touching it to a few bolts in case it was ground, nothing changed. Ideas?