Yes. There are several installation and wiring considerations that need to be addressed when changing KDM-706A units in existing installations. KDM-706A units with P/N 066-1066-20 and -22 did not originally have Mod 4 installed in original production. Mod 4 addresses the addition of a DME track flag output that is used This output is required to complete a compatible interface to some navigation systems such as the older KNS-660 and Litton 3000 as well as Sperry RD-650 HSIs. In order for a unit with Mod 4 to function properly in place of an existing KDM-706A without Mod 4, you must rewire part of the harness to prevent damage to the unit. Connector P7063 must be removed from ground potential (i.e. -20/22, non Mod 4 units) and rewired. Pin 19 of P7063 was used for aircraft ground on -20/22, non Mod 4 units. For units with Mod 4 and -23/24/25, Pin 19 is now used to provide +28VDC at 150ma drive capability for the purpose of operating a DME track valid flag. This can be achieved by connecting Pin 19 to Pin 36. Therefore, in order for units with Mod 4 as well as -24/25 units to function in place of -20/22/non Mod 4 units, you must remove pin 19 from the mating connector harness and connect it to 36 or splice into the wire going to Pin 36. For complete detailed information, reference Bendix/King Installation Bulletin # 245 and Bendix/King Service Bulletin P/N 600-04374-0040.