Help! Where does this bulb plug in at?

[87Scotty]

I'm putting my dash back together on my '87 Scottsdale. I have a bulb that I cannot figure out where it goes. It is on a single black wire about a foot long that is grounded to the ash tray. It plugs into the same type of hole that the heat/ac control and instrument panel uses but I can't find an empty one.
I've tried my service manual and wiring schematics, just can't figure it out.
Can anyone help me?