What does Overdrive do ?

[gregvl52]

not on any car I've seen overdrive

Normally overdrive is limited to the top gear and so most folks leave it on.

There is confusion with folks thinking the option to delay an auto switching up a gear is "overdrive" it is NOT

I don't quite get what you're saying. On these large, fairly modern vans, the automatic transmission would choose when to go into overdrive in the top gears only for highway cruising. What is wrong with that? People might want to disable it if, for example, they are towing something and want more power available. See this post:

I have a Windstar from about the same period. The button on the end of the shift lever does disable the overdrive. On the Windstar, there is a light on the handle of the shift lever that lights up when the overdrive is disabled. Your manual should reveal where the overdrive light on your Aerostar is.

I'm pretty sure this is a real overdrive, not just the highest gear. Admittedly, there are people who would call a top gear where the ratio is something like 0.9xx:1, such that the engine is "overdriving" the transmission, an overdrive, but I'm pretty sure that modern automatic vans have overdrive that engages automatically, decided by the transmission computer, and, like just about any electronic system, can be disabled.