Mystery bulb socket behind dash

I’ve been getting my gauges and interior lighting in my 70 Duster to work and while messing with the wiring behind the gauge cluster, I found this thing that appears to be a bulb socket, it’s got two wires going into it, a blue and a blue with white stripe. One of them goes to the circuit board connector and the other one has been chewed through by my ex. It fits perfectly into one of the circuited light holes in the back of the cluster but I thought all of those got power from the circuitry itself.
I believe the harness is out of a 71 Duster.
What is this for?
1E5290C0-17D2-4AD2-877E-BE2D7324DD7A.jpeg
Thanks guys