A Thermocouple is not the same as a thermistor and should also not be put inside thermistor pins - that gives no meaningful results. For thermocouples you need a special chip to convert data to a linear voltage. Some boards have build in support for thermocouples, then all you need to do is set the right thermocoule type in firmware (e.g. AD595, MAX 6645).
Alternatively buy a thermistor and put it into the extruder as a replacement.
