Dash/Instrument Illumination: Step by Step Search

IF YOU CAN provide a good sized photo of the rear of your cluster it will help. I do not have a source for that other than "accidently" finding such a photo on the internet. As an example, my 67 originally had two separate in-line harness connectors feeding two boards to make up the complete cluster. This means that there is at least one lamp on both boards, so one feed path might be compromised.

1...Clean and solder the harness connector pins or obtain "repop" boards. Use a good "electronic" solder and buy yourself some liquid flux which matches. "Flux pens" are a good option.
2....Loosen/ tighten the gauge nuts as they get corroded and lose contact with the board.
3...You are on your own on the gauge regulator/ limiter as I'm not familiar with early clusters
4....Get an abrasive eraser or maybe even very fine sandpaper, perhaps 500 or 1000 grit to clean the board contacts around the socket holes.
5....Clean the socket contacts or replace them, along with the bulbs I would suspect corrosion in this area, board to socket, socket to bulb, and amount of pressure at the contacts. Bend them "spring" to make them tighter contact
6....Clusters are notorious for poor grounding. Make sure boards are grounded to the cluster and add a grounding pigtail which you bolt to the dash frame or column support. Again, if you have two boards, make sure the pigtail grounds both