Voltage control Module used to adjust voltage from 14.8v to 15.8v. This connects to All high output alternators using the GM 3 pin voltage regulators (denso) using diodes off sense wire (no more with this controller). This is a Voltage control knob supplied with a digital voltage meter. Comes with: Controller WITH KNOB (not pictured) 6 foot harness with 3 pin Harness attached and instructions. Unit comes in a BLA CK BOX. DON NOT SELECT COLOR AS IT COMES ONLY IN BLACK.