This ZT AMPS Technical Bulletin explains about the remote in-trigger on the ZT amps when using 12Volt as a trigger. Many larger commercial vehicles have a 12Volt transformer that steps down 24Volt to 12Volt allowing the radio and other accessories to be fitted. Many of these accessories do not have a solid common ground. This means that when using the 12volt remote / output from the radio there isn’t a true 12 Volt trigger as there is no common ground. The ZT amps also have a differential input on the RCA’s meaning there is no common grounding threw the RCA connections. This is designed to avoid noise on the RCA’s and more importantly, to prevent causing electrical issues by creating a common ground threw the RCA’s.