HELP! Circuit board
I had a similar problem on my 1966 Barracuda. The Oil Pressure and Ammeter lights would not work and the Oil Pressure would read intermittently. After cleaning the mounting screws for the board and all the contacts, it turned out that the 3 pins the harness connects to were loose and had a poor contact to the circuit board. The pins are pushed through and tabs bent over to make them tight. Over time the tabs weaken and fall off causing the problem.
I ended up finding some small (and I mean small) screws and screwed them in from the back making the pins tight and restoring the contact of the pins to the board. I double checked the clearance to the back of the gauage assy. and put a piece of electrical tape on it as a precaution. All is functioning now.