Thanks, Eagle43. I ordered a 6V to 12V converter shipped to my door for less than $10.
It was kind of fun to read all the posts here though. I understand why 6V-12V-6V gets mixed up. Most questions here are usually on how to run old 6V things after a conversion to 12V, not the other way around.
I had an old 12V horn that I wanted to run on my original 6V car and I got my answer.
Thanks!