For reference, the orange wire to the power pack is 12v; the white wire is 200v AC output from the power pack.
Here's the method of testing the panel(removed)as per the service manual:
"Using a 12v test battery and 4 jumper wires, connect one jumper from the white wire terminal on the cluster to the white wire terminal of the test power pack. Connect another jumper wire from the base of the power pack to the negative post of the test battery. Connect a third jumper wire between the base of the power pack and the cluster housing to provide a ground. The fourth jumper wire is clipped to the orange lead of the power pack, but do not connect the free end of this wire to the battery at this time.CAUTION: do not attempt to disconnect the white wires from the gauges with the battery connected to the cluster!
Remove the wire of one gauge and touch the end of the fourth jumper wire to the positive post of the test battery. If the remaining gauges light, the disconnected gauge is faulty and must be replaced. Test each gauge until the shorted gauge is located"
I know the radio in your car is out, but if you know your power pack to be good, and the cluster is still in the car, you can check for a shorted gauge by disconnecting the white cluster wire connector behind the instrument panel. If the radio dial lights when the headlight switch is turned on, then one of the gauges is faulty.
All this is per the service manual.
If the gauge cluster checks OK, and all other electrical components in the system, (headlight switch, fuses, grounds, etc)check OK, then check the shift selector lighting strip. One spill of Coke on this thing will eventually corrode and kill them...Remove it and test it separately while you have all the test wires set up. I hope this helps somewhat.