Classic/Antique Car Repair: 1965 CORVETTE ELECTRICAL TROUBLECSHOOTING, infinite resistance, infra red thermometer

Question
New temp sending unit.  Bled the cooling system.  After driving only one block, gauge is pegged and motor is still cool to the touch.  According the schematic, it is wired correctly, however, prior owner had done some "personalized" wiring of his own.  HELP!!

Answer
OK, you say the motor is cool to the touch. I would like to know what the temperature is right around the temperature sensor. I use an infra red thermometer for this that shoots a laser like beam and the reads out digitally what the temperature is. These tools are less than a hundred buck and have lots of uses. The problem might be the wrong sensor. There were some sensors for later cars that were simply an on off sensor that helped control some emissions devices. They look similar to the coolant sensor for the gage but don't work the same. The proper sensor for your rig should show a varying resistance and the engine warms up. If the sensor shows infinite resistance when the engine is cold and then jumps to virtually no resistance when the engine begins to heat up you have a defective sensor or the wrong one.
Brad