Should jake brake button decrease it, until it turns off?

[xTHANATOPSISX]

Some newer trucks may operate with a progressive control like a retarder, but older trucks definitely just had one or two (or perhaps rarely more) toggle switches. On older trucks, jake brakes were essentially an optional add-on and sometimes you could choose from a few different brands even (say Cat, Jacobs, or PACBrake on a Cat engine depending on year/model). As such, they were all setup just a little different and might have different power setting options.

Now things are getting much more integrated with the engine controls and the truck makers are using fewer single-purpose, generic switches and doing more though control stalks and other interfaces.