Only the one is needed for certain changes. There should be two junction blocks- one is green with a black base, and the other is green with a white base. The connectors for both blocks are identical, but they are two separate canbus systems. If you got the kaodtech bypass, it is usually labeled with sleeves on each set of connector wires- green and black sleeves for the one that plugs into the green block with black base, and green and white sleeves for the one that plugs into the green block with white base.