Mercury - Tab Extension Harness Assembly 20-Foot Trim Tab Lead 84-898059T20. Overview. Longer wiring runs can make trim tab installation tricky, especially on big consoles or wide transoms. The Mercury 84-898059T20 Tab Extension Harness Assembly adds a full twenty feet of reach, giving you plenty of room to route the tab wiring cleanly from the helm to the actuators or control modules. It keeps the rigging neat, avoids overstretching the original harness, and helps the tab system operate smoothl