I have had little luck with GE, Ericsson, Comnet, M/A-COM, Tyco, Harris EV Charger. It is one of the many poor performing products that have been sold over the years. I do know that depending on what model radio you use with this charger, you may need to update the feature code of the radio to operate with the external control head. I remember that I needed this for a MRK.
Sorry that I don't have the harness answer. I would need to get back to you on this.