From page 8-165 in the Dodge Chassis Service Manual for 1971, Fig. 22 - Instrument Panel Accessory Wiring - Coronet and Charger.


I believe the earlier black glove box inserts had a relief line in the form of a circle molded into the side reflecting where the switch was to be placed. It is in this location -




Whether Plymouths were similar, I can't say but the Roadrunner did share many of the same parts.

And they were located in the glove box so that they could be locked away preventing valet access to the trunk in the circumstance you were attending an affair with valet parking (since ignition and glove box keys were different).