Thermocouples have types and colors. e.g. J,K, R, S, T where K is the most common. The outer jacket is yellow for K.
Probes come in grounded and ungrounded configurations. Wires can have a junction made on them. i won;t talk about making a junction.
With a thermocouple meter that can read room temperature, some can't, any wire across the thermocouple inputs will read room temperature.
K or Chromel-Alumel. Red is the negative lead. I forget the other color. Lots of info on
www.omega.com Red is universally negative.
Another word: Extension wire
Extension wire for K thermocouples will look like copper wire. it's not. It's also NOT to be used as the thermocouple. It's only supposed to be used to extend the wire to the thermocouple.
A K thermocouple connector will have a yellow housing and come in at least two sizes. These connectors are designed to be isothermal or to keep both connections at the same temperature and have the electrical properties only of a real thermocouple at least at room temperature.
You select a thermocouple type by it's temperature range and environment it will be in.
"T" is good for cryogenic and room temperature. "C" for very high temperatures like for melting copper.
When we talk about probes, we can also talk about wells. If you wanted say a C thermocuple probe in a tantalum well. This makes the well replaceable.
The right type thermocouple for the instrument connected backwards means when you heat the TC, the temperature goes down and not up.