Where does this light socket/bulb go?

[sandorjoben]

I have a 1987 GMC V15 4x4, gauge cluster has speedo, fuel, volts, oil pressure and engine temp. I just got the truck not all that long ago, and noticed that when I engage the 4wd there is a small light that comes on that's hanging down amongst the mess of wires behind the lower dash near the fuse block and e-brake pedal, it's not attached to anything and just kinda floating around amongst the wires behind there. The socket is similar to the type that plugs into the gauge cluster to illuminate the speedometer, fuel, oil pressure, etc. only it has (+) and (-) wire and uses a GE168 type bulb. Does anyone know where this is actually supposed to go? Like I said it only comes on when the 4x4 is engaged. If need be I'll try to post a pic later. Thanks in advance.

Dave