Brad, that "solid wire" is a very fine tube with a hole about the size of a pin, because the end gets "mushed" when the end is broken off you can't see the "hollow", this is a vbery common situation with the mechanical style gauges - a wire would be plastic coated like the rest of the wires in the truck, and you'd only have an electric gauge if someone recently replaced it
edit: that fitting is a temperature sender from the engine which is where a later-than-1950 electrical style gauge would connect
[and
here's a working link]
Bill
