I also recently replaced the PCB on my '71 Monte. All the lights work, turn signals and such. As others have mentioned the fuel gauge and temp gauges do not work. The temp gauge pins out and the fuel gauge does not move. At first, if I banged on the dash, they connected and worked. This was an intermittent fix and is no longer effective. That made me think I had a loose connection. I took the nuts and washers off both and reconnected them thinking they were loose and still they do not work. I am guessing the ground is good or the lights and such would not work. I replaced the PCB because over time working on the dash it was physically damaged at the voltage meter and that light point. By the way I installed all new LED bulbs, and it looks great at night.
As anyone knows that has worked on this issue, it is a royal pain taking the dash and gauge cluster apart. Also, the PCB is fairly fragile, and I don't want to damage it. In the vernacular, "it ain't cheap".
I appreciate the long explanation MCFAN and will try each step and let you know if I am successful getting both gauges working.
