Convertible interior light?
There was a courtesy light harness (might have been optional) that plugged into the main harness and into the door switches. The light was over on the right hand side. I had a 65 Coronet convertible that I parted out and it had a pair of courtesy lights included with the power top harness. They were in the rear panels down low under the window handles. Needless to say I saved that harness for my GT convertible even though they never had that option. Got a couple of the original lights/harness if you're interested.