Would have to be ignition switch illumination. Yellow wire is dome lamp, hot at all times.
The shift indicator lamp is on a orange wire, hot from headlight switch on.
The line seems to go to the key lock light. Mopar put plugs on the front wiring harness for fender mounted turn signals whether they were installed or not. IDK for sure. This may be the same sort of thing where the wire was run whether the car had the column light or not.
My car had the column light for sure because i have the original steering column here too, i will see these days where i have to put this wire on thx peter