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That's the coolant temp sensor. You still have the original one, which is a steaming pile of monkey plop. Not so much the sensor itself, as the connector it used. It was a kinda "coaxial" looking thing, and ... it crumbles to dust along with the wires. They spooooged it with some kinda crap that eats the wires, and all the insulation falls off, just like you see there. In fact yours is in the best shape I've seen one of those for 40 years now.
All the replacement ones use a different connector. In fact you can buy them with the new connector in the box. If you buy it, make sure the connector is in there. https://www.autozone.com/engine-mana...102/248732_0_0 DO NOT use the Scothlocks; use solder, then heat shrink, then tape. Doesn't matter which wire goes to which.