Do your Scout gauges (Oil Pressure, Water Temp and Fuel) work perfectly?

Would you like them to?

Some Scout owners spend hundreds of dollars replacing the factory gauges with after market gauges. If you prefer to keep your factory gauges, I can show you how to make them work perfectly!

If you are a casual technician, you may wish to skip the Theroy section and go directly to the trouble shooting or jump start section.

• Theory
• Battery voltage in a car can vary under ideal conditions from 8 volts to 15 volts. Also, fluid levels and pressures can fluctuate wildly and quickly. Certain gauge types can give inaccurate and unreliable readings.
• IH (like many other manufactures) selected thermal gauges with a thermal/voltage regulator to overcome both the varying voltages and the rapid fluxuation.
• 5V regulator; Many technicians with a volt meter or test light can look at a normal operating instrument 5v regulator and see every thing EXCEPT 5Volts. What they see instead is a pulsing voltage which is a zero volts and then pulses to battery voltage and back to zero. Attempts to �average� this electrically with resistor and capacitor circuits are worthless since what is important about this voltage is it�s �heating� value or �RMS� value, not it�s average value. Even modern �True RMS� reading meters can�t read it since they are built to read true RMS on AC voltage of much higher frequency. If you want at True RMS reading voltmeter to measure the voltage from this 1930�s technology regulator, I will tell you later how to build one.
• What is important about this voltage is it�s �Heating Value�. That is, a resistive device connected to this voltage will heat as if it were connected to a 5V constant source.
• Inside this regulator is a dual-bimetalic strip. That is, a bimetallic strip bends as it is heated, but this �dual� bimetallic strip is designed to ignore it�s temperature. That is, the two halves counter act the bending of each other, thus at 30deg temp, the first is bent to an� angle of 5 deg and the other is bent back the exact same amount. At 130 deg temp, the fisrt is bent to an angle of 20 deg, and the other is bent back at the exact same angle.
• The two strips together are connected to a set of contacts which pass current through a heater (15.2 Ohms) wrapped around not both, but only one of the two strips causing only ONE strip to heat and deflect. Indeed, when you heat only one of the two strips, the result is that the combination of the two does indeed deflect. This is designed to open the contacts and remove the heat to the one strip when the heating voltage applied to this heater is 5 Volts. Next, the heated strip cools and the contact come back together, again and again. The resulting pulsing battery voltage has a �heating value� of 5 volts always.
• This regulated 5 Volts of heating capability is applied to three gauges in the Scout; Fuel, Oil and Temp. Each of these gauges is built with identical dual bimetallic strips. Each of those strips bend with ambient temperature (one canceling the other) such that no deflection of the red needle is caused. For this reason, on a cold morning or hot afternoon, your gauges do not move simply because of the temperature of the air.
• In each gauge however, one of the dual bimetallic strips is wrapped with a heater (again, 15.2 Ohms) which is in series with the wiring of the chasis and a sending unit in the motor or fuel tank.
• As the sending unit resistance changes from 100 Ohms to 5 Ohms, the respective gauge moves from left to right, regardless of ambient tempature or battery voltage.

• Common failures and their causes
• Sending Unit Failures
• Open wiring
• Shorted wiring
• Open voltage regulator
• Open firewall plug
• Burned up gauge (heater)

• Jump start
• Voltage Regulator Replace
• Clean 3/8� nut connectors to circuitboard on back of gauges
• Replace sending units (temp and pressure)
• Detailed description