Many of the existing TSO C91a installations with Joliet, Pointer and Narco 121.5 MHz ELTs utilize only 2 wires between the cockpit remote switch and the ELT. Other manufacturers of 121.5 MHz ELTs use 3 or 4 wires. The Artex 2-Wire Remote Interface uses just 2 of the existing wires from the wiring harness to connect the new cockpit remote switch to an Artex 406 MHz ELT for a simplified, cost-efficient upgrade.