Also known as a treble bypass kit. It is useful to maintain your highs when you roll back your volume control. But remember it does brighten your overall sound when at full volume. It is most useful on high output pickups. We do not use it with our vintage wind Fralins. The kit is offered unwired or prewired. It is an easy cheap experiment for those who want to tinker. It is wired between the middle and outside input leg of your volume control.