You take one set of rcas from your head unit. Plug it into the back and then send one set out to an amp. It is very cool looking to me. The item "RARE USED OLD SCHOOL DENON DSV-1 VOLUME LEVEL METER VERY COOL LOOKING FREE SHIP" is in sale since Wednesday, February 17, 2021. This item is in the category "Consumer Electronics\Vehicle Electronics & GPS\Car Audio\Car Audio In-Dash Units".The seller is "andy4879" and is located in Cleveland, Georgia. This item can be shipped worldwide.