This voltage boost harness fits 1996-2004 GM Trucks and SUV's with oval GM alternator plug. The longer blue wire gets connected to an ignition switched 12V+ source to turn the alternator on and off with ignition. This harness can be used with stock alternator harnesses on 1996-2004 GM trucks with oval 4 pin alternator plug, and can also be modified and hardwired to ignition 12V+ for engine swap applications where the stock alternator harness is not available. NOTE: This unit is NOT FOR USE ON STANDARD 12V AGM BATTERIES. This module will increase the charging voltage .5V to 1.0 Volts, depending on application, and will swell and damage AGM batteries. Please check with your Lithium battery manufacturer to verify the proper charging voltage before installing this module!