another temp gauge/fuel gauge/voltage regulator thread

There's a lot of bad advice in this blog, jumping to conclusions with no troubleshooting at all. If I had that car I would pull the instrument panel out of the car and get things working on the bench. It sounds like your instrument voltage regulator is the place to start. Since it's a Valiant the IVR is external to the gauges and easy to get to. Usually I find the "fingers" holding the IVR are not holding it in well and not making good electrical contact so it has to be fixed out of the car. You'll need to feed 14 volts to the input of the IVR then check the output which is a rather crude pulse code modulated output to emulate 6 volts for the fuel and temperature gauges. If you connect a 10 ohm resistor from ground to the opposite side of each gauge you should get full deflection. If not the circuit is open or you're not getting output from the IVR. If things are working at the bench then you either have wiring issues to the sensors or the sensors are not working properly. In any case, it's a simple series circuit and should not be difficult to fix.