Here is a really great writeup for the gauge, according the data here somehow the gauge is bad.. http://www.panteraplace.com/page205.htm . But not too hard to do some measurements;
- disconnect the sensor and measure the voltage of the wire...this is the open "TERM" voltage which should be about 5volts to ground.
- attach that 39 ohm resistor between the wire and ground (not to the sensor), you should measure about 3v and the meter should be somewhere at the 'second mark' and 190'.
Bottom line, you should be able to change the resistance between the TERM wire and ground and make the meter read whatever you want, or the gauge is broke.....According to the PanteraPlace data, there is no way a healthy gauge with a 39ohm resistor in series should cause the gauge to peg out at the 260' (2:00 position), at most it should be around half way.
The gauges are so simple, I don't know how they would wear out to cause a swing to dead right...(Just thanks to the incredible writeup by Bill Taylor here! And good news, a replacement Temp gauge with any bezel but half-V black is easy to find...)--Lee