Batboard

I recently obtained a syntor X9000 control head cable with a training wire attached to pin 13 (Mic Low) at the radio side. Can anyone advise why there would be a set-up like this? I cannot find where it may need to be grounded or connected to something.

Thanks

I can not think of any reason for the added wire. Just cut it off near the connector and insulate the end of the wire.