gauge voltage limiters

I also have never seen a 69 Barracuda without a Rally dash. Here is why the fuel, oil and temp gauges are not working. I would bet the farm the IVR (Instrument Voltage Regulator) in your car is built into the gas gauge. The oil pressure and temp gauges need a power feed from the IVR in the Fuel gauge. Here is how it all works. The fuel gauge has 3 wires on the back, and the oil and temp gauges only have two wires. One of the three wires on the back of the gas gauge is 12 volts power in. That current goes to the IVR inside the gas gauge. The IVR changes the 12 volt current to about 5 volts by opening and closing some points fairly rapidly. The result is a pulsing current of about 5 volts. That 5 volts from the IVR powers the Gas Gauge and goes out to the oil and temp gauges through the second wire on the back of the gas gauge (look at a wiring diagram). The third wire on the back of the gas gauge goes to the sending unit in the fuel tank. When the fuel tank is full, the float is up, and the resistor in the sending unit allows full current (about 5 volts) to flow through to the ground (that is why the tank has to be grounded). When that current is flowing, it flows from the IVR, through the bi-metal strip in the gas gauge attached to the needle and through the sending unit to the ground. The bi-metal strip heats up a little and the needle moves up to full. As the fuel level goes down, the resistor in the sending unit allows less current to flow through the gas gauge. Less current flow means less needle deflection. When the tank is empty, there is no current flow, so the needle will not move off of empty. The oil and fuel gauges work the same way. One of the wires on the back of each gauge is a power in from the IVR, and the other is power out to the appropriate sending unit. When oil pressure or temperature is high, the sending units allow current to flow through the gauge, through the sending unit and into a ground. When oil pressure or temp is low, little or no current flows through the sending unit, so there is little or no movement in the gauge needles. You either need to have the gas gauge repaired, buy a new gas gauge, or re-wire to add a separate IVR. Also, I bet that your Alternator gauge works since it is on a separate circuit. If you have any further questions, feel free to send me a PM.