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Everything you want to know about the center console
gauges
Content is not complete
Miscellaneous Information
- 1977 was the first year for the new center cluster
and console that accepted a standard GM radio. The connections
between the gauges and the wiring was through a flex circuit. It
is prone to cracking and poor connections. New ones are available.
The 77-80 had a very similar console. The gauges had white pointers after 77.
77 gauges are unique for this reason.
- 81-82 - Clock replaced with Oil Temperature Gauge.
No change to flex circuit. New mounting plate. New bezel.
Round opening for clock is now like the others. Bottom is flat.
This console will not mount on a 77.
- Calibration Resistors - Don't mix them up! They
are color coded. The go in specific locations. They must be
installed exactly as they were removed. Make sure you take
pictures or notes if you remove the console to work on the gauges.
- Resistors are year specific in some cases. For
example, larger gas tank cars will have a
different resistor on the fuel gauge.
Temperature Gauge
The sensor is a variable resistor. The outside case is grounded at the
engine. The terminal goes to pin 20 on the PC board and on to the gauge.
So you need to make a connection from the sensor case to the ground on the
gauge for testing.
The Gauge has 4 posts but only 3 connect to the outside.
If you are looking at the face as it would be in installed in the dash,
here are the connections:
12 o'clock - Should be Switched 12V - Flex circuit to Pink wire.
9 o'clock - Should be Ground - Flex circuit to Black wire on connector.
6 o'clock - Certain that it is the wire to sensor - Flex circuit to
Dark Green wire on connector.
3 o'clock - is not connected to the flex circuit. It is used to
calibrate the gauge. There's an external resistor that goes from this post
to the post at 9 o'clock.
Calibration Resistors
All the gauges have a calibration resistor on the rear. It is below the
flex circuit but can be seen though an opening. Your gauge should have
come with one. It's a flat ceramic rectangle shape with some color. Orange, blue, green, etc. Changing the value of this resistor will move
the gauge up and down it's range. Lower resistance moves it one way.
Higher resistance moves it the other way.
Disclaimer: I have never found this documented anywhere. It is not in
the electrical troubleshooting manual. The color codes are not in the
assembly manual. This is by trial and error testing and comparing other
known unmolested gauge clusters.
Example of a resistor installed on the rear of a gauge
Colors / Measured Values
- Light Blue - 125 ohms
- Green - 90 ohms
- Dark Blue - 83 ohms
- Red or Orange - 85 ohms
- Yellow - ?
- Pink - ?
Volt
- The Light Blue (125 ohm) is used on the Volt gauge.
- If you use
something with less ohms, the voltage reads higher.
- With a Green (90 ohm)
resistor, the reading jumps to 18 volts from a normal 13.5V.
Water Temperature
- Red (85 ohms) is used on the water temperature gauge.
- Less ohms = lower reading
- If you lower the
resistor to about 40 ohms (testing) the reading will lower 25 - 40
degrees.
- I have also seen Yellow on the temperature
gauge in an original 1980 Vette. I don't know the value.
Oil Pressure
- Dark Blue (83 ohms) is used on the oil gauge.
- Oil - Less ohms = higher reading
- If you lower the resistance to 40 ohms (test) the reading will
jump from the normal 30 to 60
- I have also seen Pink on the oil gauge in an original 1980 Vette.
I don't know the values.
Gas Gauge
- Green (90 ohms) is used on the 77 Gas Gauge.
- Less ohms = lower reading
- Green on a 77 with a 17
gallon tank causes the low fuel light to come on with slightly over 4
gallons in the tank and read full with a full tank.
- If you put a Red (85
ohm) on this gauge, the low fuel light comes on at about 2 gallons but the
gauge never reads completely full. Red might be the right one to use on
the later C3's that have the 24 gallon tank.
Connection info for the temperature gauge
The sensor is a variable resistor. The outside case is grounded at the
engine. The terminal goes to pin 20 on the PC board and on to the gauge.
So you need to make a connection from the sensor case to the ground on
the gauge for testing.
The Gauge has 4 posts but only 3 connect to the outside.
If you are looking at the face as it would be in installed in the dash,
here are the connections:
12 o'clock - Should be Switched 12V - Flex circuit to Pink wire.
9 o'clock - Should be Ground - Flex circuit to Black wire on connector.
6 o'clock - Certain that it is the wire to sensor - Flex circuit to Dark
Green wire on connector.
3 o'clock - is not connected to the flex circuit. It is used to calibrate
the gauge. There's an external resistor that goes from this post to the
post at 9 o'clock.
Mounting Oil Temperature Gauge instead of the clock - 77-80 cluster.
81 or 82 had an oil temperature gauge in
place of the clock. It would be an easy change and you wouldn't have to
fabricate a thing. You could probably use the sensor.
Since the clock is on a separate plate, you simply remove the clock and
plate then slide in the new plate and oil temperature gauge. No modifications to
the remaining cluster required. Note that the clock opening is
round. The other gauges have a flat bottom part. I'm not sure
how the oil temperature gauge will look when installed.
You can not use the bezel from an 81 or 82 in the 77.
It won't mount to the dash pads. The shape is different.
Troubleshooting
- Oil Pressure Gauge - An open wire or flex circuit to
the sensor will cause the pressure to peg to the right. Ground the
end and it should return to 0
- Water Temperature Gauge - An open wire or flex
circuit keep the gauge at rest. Ground the end of the sensor and
the gauge will peg to the right.
- Sensors must be grounded through their threads to the
block to work. It is not recommended to use Teflon tape for
sealing them. It could block the ground.
- Bouncy? Gauge is worn out. The needle should
have some mechanical resistance when you try to move it with your finger.
This problem will be very noticeable with the
fuel gauge. As you drive and the gasoline sloshes around in the
tank, the gauge is very busy trying to keep up!
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