From a NOS Autolite switch service replacement, and what I recall on other original switches, you should find a tag wrapped around the harness closer to the switch. See image of my 67 tilt column switch.
Since posted in the Mercury (non-Mustang) section, I assume you are looking to find a part number for your 68 Park Lane (you did not specify)
Engineering number on your Mercury will follow the typical Ford numbering process. Cxxx-xxxx-x pattern.
For what it is worth, the number off the tag will USUALLY NOT match the PART NUMBER Ford used for servicing the switch. For example, the switch pictured below has a tag with engineering number of C7ZA-13B302-E while the Autolite service box has part number C7ZZ-13341-E on it (some discrepency on this since the suffix "E" is hand written over a "-02") The point I am trying to make is you need to source your "most correct" Service PART NUMBER from a Ford Master Part Catalog (MPC), and unless the catalog directs you to look at identifying "tag" number, your REPLACEMENT number should be easily found in the most "period correct" MPC you can locate. Later MPC sources will find the most recent number Ford gave to the service replacement part number, usually a more "generic" fitment service part.