I had the dash out of my 79 GT t0 fix the heater control and while in there I changed the regulator for the gauges that was reading slightly different each time. I used a part from Macs; 64-42672. replacement for Ford C9AZ-10804-A . Thought this finally cured the gauge issue. After a month when first starting the fuel and oil gauges slowly move upward then a minute or two just go back to where they are when the key is off. Next start they may work or not, one minute they are up, next look back they are dropping off. Somewhere I read these are poor quality regulators. Who sells decent ones that work? It kinds of unnerving to look at the oil pressure gauge while driving and have the gauge show nothing. The problem has to be that regulator.