Actually, on the PDF instructions, it says:
    The RCA audio connections on the GMKENX provide an audio input to your GM radio for use with any device that has RCA line level outputs. This feature is perfectly suited for Multimedia devices such as VCRs, DVD's, Game Systems or TV tuners. Portable music players such as MP3, MD and CD players can utilize this input as well. To activate this input you simply need to wire the GRAY wire from the GMKENX to a toggle switch that will ground the GRAY wire when selected. When the GRAY wire is grounded the CD changer will be automatically paused and audio from your auxiliary device will then be heard. When the GRAY wire is ungrounded CD changer operation will resume where it left off.
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Bitt Faulk