Did Trump say “Ford / General Motors / GM” at St. Clair County, Michigan?

Yes. Said at 4:29:29 PM ET, flagged live 0.70 seconds after the word.

“An old I think it's a 19 o one building ford”

From Saidwire’s live log of Trump rally · St. Clair County, Michigan. All 13 words said at this event.