This information was written for a 1965 Vette but should apply to all 1963-1967 Vettes. Only thing different will be wire color and you will need to substitute correct wire colors.

I used the word "CALIBRATE" but also could have used "SET", "ADJUST" or "CHECK" so substitute whatever one that seem to work best for you.

Calibrating Fuel Gauge Needle

There are 3 terminals looking at the back 3, 6 and 9 o’clock. The 6 o’clock is mounting and grounding stud.

This calibration is to get pointer (needle) set and does not include fuel sending unit which when connected may not produce accurate results.

Three wires are needed.

With the 6 o'clock stud grounded apply 12 volts to the BLACK/PINK wire (3 o’clock) and ground to TAN wire (9 o’clock) the needle should go to FULL mark  (exactly), then reverse the wires (3 & 9 o'clock) it will go to EMPTY (or lower).

If not pull the needle and apply 12 volts to 3 o'clock and ground 9 o'clock and put needle on FULL. It's ok to let needle go below EMPTY.

Be careful when pulling the needle and gently press when reinstalling as those old core movements get pretty fragile in the years.

Calibrating Temp Gauge Needle

The BLACK/PINK (12 o'clock) wire feeds a constant 12V to a coil in the gauge, and the other end of the coil is connected through the GREEN (6 o'clock) wire to the temp sender. The temp sender contains a thermistor (variable-resistance element) whose resistance to ground changes with temperature. As the temperature goes up, the resistance goes down, increasing current flow through the coil to ground, which moves the needle to the right.
 

This calibration is to get pointer (needle) set and does not include temp sender which when connected may not produce accurate results.

In Car -- (To see if gauge is working correctly)

With the key in "on" or "accessory", disconnect the DARK GREEN wire at the sender - the gauge should peg to full cold (infinite resistance). Then ground the sender wire connector to the engine, and the gauge should peg to hot (zero resistance).
 

Bench Test

Three wires are needed.

Ground 3 o'clock or cluster if mounted

Then Apply 12 volts to BLACK/PINK (12 o'clock)

Should read COLD

Then Ground DARK GREEN (6 o'clock)

Should read HOT

** note ** 9 o'clock not used

To calibrate pointer (needle):
Note where pointer is for COLD & HOT readings and center using those two points.

Be careful when pulling the needle and gently press when reinstalling as those old  core movements get pretty fragile in the years.

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