Mercury - GPS Extension Cable 6.6-Foot CAN P Line 84-879171T22. Overview. Some boats need a little more room to place the GPS antenna where it actually gets clean sky. The Mercury 84-879171T22 Extension Cable adds 6.6 feet of length to the GPS line used with the 8M0024918 kit, giving you the flexibility to route the antenna to a better spot without fighting tight bends or short harness runs. It's made for CAN P GPS systems on boats without an Auto Pilot module, and once connected, the system sim