Dash Gauges

Gauge failures are often caused by defective wiring or grounds. The first step in locating trouble should be a thorough inspection of all wiring, terminals and printed circuits. If wiring is secured by clamps, ensure the insulation has not been severed, thereby grounding the wire. In the case of a fuel gauge installation, rust may cause failure by corrosion at the ground connection of the tank unit.

CONSTANT VOLTAGE REGULATOR GAUGE SYSTEM (CVR)

The Constant Voltage Regulator (CVR) type indicator is a bimetal-resistance type system consisting of an Instrument Voltage Regulator (IVR), an indicator gauge, and a variable resistance sending unit. Current to the system is applied to gauge terminals by the IVR, which maintains an average-pulsating value of 5 volts.
The indicator gauge consists of a pointer which is attached to a wire-wound bimetal strip. Current passing through the coil heats the bimetal strip, causing the pointer to move. As more current passes through the coil, heat increases, moving the pointer farther.
The circuit is completed through a sending unit which contains a variable resistor. When resistance is high, less current is allowed to pass through the gauge, and the pointer moves very little. As resistance decreases due to changing conditions in system being monitored, more current passes through gauge coil, causing pointer to move farther. Do not apply battery voltage to system or ground output terminals of IVR, as damage to system components or wiring circuits may result.
The gauge pointer on CVR systems will drop below the low mark when the ignition is turned Off.

MAGNETIC GAUGE SYSTEM

The magnetic gauge system consists of the sending unit and a magnetic gauge. This system does not use the instrument voltage regulator (IVR) used in other systems. When engine oil pressure or coolant temperature is low, the sending unit resistance is high, thus restricting current flow through the gauge, allowing the pointer to move a short distance. As engine oil pressure or coolant temperature increases, the sending unit resistance decreases, causing an increased current flow through the sender and a higher movement of the pointer.
The gauge pointer of the magnetic system remains in position when the ignition is turned Off. It will move to the correct position when the ignition is turned On.