1965 Thunderbird Ignition Switch Issue

[Kartman01]

I have a ‘65 Thunderbird convertible with a puzzling ignition switch issue. Periodically, the car will not turn off using the ignition switch. I have replaced the complete switch assembly twice (new replacement unit from Larry’s Thunderbird) and it will work fine for a while and acts up again.

Are there any other potential causes for this issue - aside from the ignition switch?

Thanks in advance for any help!