'66 'Cuda gauges not working

Hi all, I'm trying to wrap up a mild restoration on a '66 Barracuda and the gauges have me stumped. They used to work ok(temp, gas, and oil pressure), then worked intermittently, then they worked intermittently and no gas gauge at all, and now none work. Every time I pull the dash out to investigate and reinstall, they would briefly work. Now they won't work at all and I'm at a loss. Gas sending unit is putting out a signal, power is getting to the gauges, gauge works when supplied with power, and there are brand new circuit boards. As far as I can trace, everything has a good connection.

Where should I look next? This might have been covered before somewhere but I genuinely don't have the time to read through all the threads. Thanks in advance!