6 or 12?

As I understand IH light truck history, 1956 was a transition year. Trucks started out, I have been told, on 6V positive ground. Then, the story continues, the first of the 12V trucks were also positive ground. But before the model year completed, they all transitioned to 12V negative ground. I'm not 100% sure if this is true, but it IS the story I have heard. in 1956 I was 2 years old, so I don't have firsthand experience to report.