Gauge Cluster Issues, Where to start?

[pjmoreland]

Nice satisfying find there.

Only four of the bulbs are for backlighting. With the lights on, reach up under the dash and twist one of the bulb sockets at a time to disable it. You should see diminished light for each bulb you twist. If you don't see diminished light, then that's your culprit. The bulb socket contacts tend to get crusty. Pulling the bulb out of the socket and reinstalling it 10-20 times can help. The socket that is above the battery gauge is the most likely suspect.