On the wagon or off the wagon?

Factual Questions
1

on or off the wagon?

I asked someone the other day if they were still on the wagon (She was cutting smoking out). But then realized that everyone has a different way of looking at it and that my own view is muddled. I know it originates with drinking (I should say I think) but also applies to other assorted misbehaviors.
When are you on the wagon?, when you are drinking, or are not. And what is the origin of the phrase?

2

“On the wagon” means that you are not drinking. I always assumed that it had historical roots in the Temperance Movement. Maybe they rode reformed drunks around town on a wagon to advertise their cause?

3

“On the wagon” comes from “on the water wagon”,a term to indicate that you’ve given up “John Barleycorn” for more temperate ways.