Well I figured out that the gauge resistors are wire wound and have different colors per Toms thread on the gauges.
http://67-72chevytrucks.com/vboard/s...d.php?t=640615
I assume you have seen my posts on the temperature gauges where the resistors are added to lower the gauge readings, but I will add it here for the other viewers.
And this
Are you able to take an ohm reading on your sender when the engine is hot and when it is cold? Meter leads on the terminal connection and the engine block. Make sure the sender body reads zero ohms to the block as well. Some types of Teflon tape will give higher than normal readings on the gauge.
Is this the correct sender IOW you have not converted from a three gauge dash? And your engine is running at the correct temperature?
You can remove the resistor and measure the resistance with the meter for an accurate reading.