This plugin is maintained by the BakkesMod team.
This plugin (which only works in freeplay and replays) displays the hitboxes for all the boost pads. It also shows a small dot on your car indicating the exact location that the hitbox is checking. This is shown in the first gif.
The second gif shows the customization options: you can display the whole hitbox instead of just a ring, and you can change the color and opacity of the hitbox/ring.
Click on either gif to go to its HD gfycat link