Why do you need a transponder?
If you file the appropriate flight plan and land to clear US Customs, I
don't understand why you would need one.
I fly a 1945 Aeronca Champ with no electical system, is there some new
rule that mandates a transponder for transborder operation?

Victor wrote:
On a trip to Mexico my transponder failed. How can I cross back into
the US with a failed transponder.