The Icom internal relay have low current contact ratings and becomes problematic in most shack conditions. This cable simply plugs into the accessory (ACC 1 or ACC 2) rear jack (DIN type) on the Icom.  Five feet of shielded cable and an RCA/Phono type plug fits to your amplifier.

This cable will also work as a buffer relay with the following Icoms: 725, 726, 728, 729, 735, 736, 737, 746 Non-Pro and PRO, 756 Non Pro and Pro (I, II, III), 761, 765, 775, 781, 7600, 7610, 7700, 7800

This package is compact and streamline, all components located inside the connectors. Unlike other solutions, there is no klunky external box and no need to apply other external power. Althought there's a relay inside the DIN connector, it looks like an ordinary cable.

For the technical types, the circuit uses voltages available on two pins of the radio's accessory jack for switching. The relay contacts are rated for 2 amps DC and 0.6 amps AC, more than sufficient for many amplifiers (Such as Heath SB220, Collins 30L1, 30S1, Henry 2K, Ameritron AL-80/82/811/1200/1500, Dentron GLA-1000, QRO, etc.).