InstInstrument Panel Wiring Question, What is This?

[Ironangel]

Ok, I replaced the old dash "after" removing the instrument panel,radio,ash tray,defroster vents and glove box lid. I damaged the glove box liner removing it. There is single wire leading to a single twist in bulb/socket. All the other twist in single unit bulbs are energized off the circuit board/sheet. The bulb socket in question was white instead of black like the others. It also had "Strange" steel clip molded into the top of the twist in socket. What is this and why is it engineered like that? I busted it also removing it from the panel. One more question, Is one bulb socket opening supposed to open on the back of the gauge cluster? I can see "TEMP" inside the bulb opening. My truck has a mechanical temperature gauge, so does the factory skip that bulb or is it missing? Heres some pics and Thanks for the help you guys!