That short piece of pipe between the compressor housing and actuator. All the boost controller does is 'fool' the actuator by changing the pressure. Works much like a valve on a compressor really. I am ofcourse talking about a mechanical boost controller.
You can T-piece that pipe and take a pipe from there all the way to the inside of the cab and put your controller under your steering or somewhere so you don't have to stop and set it, you can set it while you drive, this means you have full control of your boost, should you need more or less just reach down and change the setting.
