I've got the Greddy turbo timer and my girlfirend has the HKS turbo timer (on her 95 TSi AWD, shit that sucks, it's so fast) and they are both the same more or less. The harness that come seperate is a "Y" shape. You unplug the factory harness that goes into the ignition and plug in the harness from the timer. then plug the factory harness into the the other end of the timer harness. Then you plug the harness from the actual turbo timer into the the one plug left open on the turbo timer harness. Then just ground it and start it up. Note, the HKS timer wouldn't work until the safety wire was attached to the parking brake. Hope this helps.