Mercury - MP Alert Add-A-Light Kit (Oval) Expansion Light & Y-Harness 8M0109505. Overview. If you're running the Mercury Moving Prop (MP Alert) system and want even better visibility around the transom, this kit makes it easy to expand. The Mercury 8M0109505 MP Alert Add-A-Light Kit lets you add an extra oval smart light-ideal for boats with wide swim platforms, stepped transoms, or layouts where two lights aren't enough. With the included Y-harness, the new light plugs right into the existing s