The blue TACH lead is designed to shut the GlobalCruise down if you accidentally put the shifter in Neutral (automatic transmission). This lead is tied into the neutral safety switch. Hook up the battery and turn the ignition switch on. Using a circuit tester, determine which lead is "live" when the shifter is in Park or Neutral. Should the shifter be bumped into Neutral, GlobalCruise shuts down, which keeps the engine from over-revving. Feed the throttle cable through the same grommet the TACH lead comes through.