The sheathing and length sounds like one of the 2 rear wheel emergency brake cables but the ends do not look correct. Is there a cable used at the emergency brake lever in your car? My Canadian car does not have the floor lever emergency brake so not sure what is connected under the floor to the main emergency brake assembly but certainly looks emergency brake related but maybe aftermarket...
1938 Canadian Pontiac Business Coupe (aka a 1938 Chevy Coupe with Pontiac shaped front sheet metal - almost all Chevy!) 1975 4-speed L82 Vette
My “educated” guess is that it is one of the 2 cables that go between the radio box and the control head that mounts in the dash. Not sure what year or years it would fit.
That explains that. My car had an old Philco radio cob up under the dash when I bought, There was no in dash head. Just something rigged up to work. Thank you for all your help!