Thank you for contacting our support forum. Please see the attached document for details on the 3 wire harness (HRN-CW03S3) including installation steps. This document contains the details that we provide to the public. Any further details, such as pin-outs of the GO7 device, are proprietary to Geotab and cannot be shared publicly.
Hope this helps.
HRN-CW03S3 Install Guide (1).pdf