I need to know the wiring procedures for Kenwood hand held radio to a helmet

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I have a mechanic that uses a Kenwood handheld tk210 that wants a transmit switch betwwen his helmet and the radio so he can talk to the pilot outside the helicopter. the accessory cord for the radio has a jack that looks like for phones and the other looks like transmit but I have hooked up every direction I can and it will not transmit thru the switch