This is an excellent question. I reached out to some manufacturers and their tech's didn't know, so I did a little more research to help.
For an air brake motor coach, when you hit the engine brake or jake brake the engine slows the vehicle by opening exhaust valves in your cylinders while at the top of the compression stroke versus using the air brake system to slow the vehicle using the air brake system. The brake lights still need to light in most states because you are decelerating,... view full answer...