Active Trim kit 8M0129439 includes the Electronic Control Unit (ECU) and connecting harness. The function of the Active Trim is controlled on the screen of your Mercury VesselView 403, 502,703 or 903. It is compatible with a Lowrance or Simrad displays using the VesselView Link. Active Trim kit 8M0129439 is only for use with single engine installations of Mercury 150hp 4-stroke outboard or 150-250hp OptiMax outboard with the Mercury VesselView System. Installation may require additional parts depending on boat rigging.