1985 K10 4x4 question

[Vietnamvet]

I have been rewiring my Brother-In-Laws truck since all the wires were cut and non-functional.

I am down to one wire that I cannot find in the shop manual or 85 wiring diagrams.

Wire appears to ground at the ash tray housing/dash with a light bulb on the other end of the wire.

Just guessing, I would say that it goes to 1. Radio 2. Heater/AC Control but can't find a position for it. I guess it could go to the Instrument Cluster but again, what position.

I have added a picture. If you can tell me where the light goes would be of great assistance.,

Thanks in advance