Both the GMR 18 and the GMR 18 HD use an ethernet cable to talk to the network. Garmin says in their manual not to shorten them, but they sell a field installable connector to do just that. They even gave me one in the box with my unit. It will not hurt to shorten the cable just void the warranty of the cable. I haven't shortened mine but now that the warranty is gone I will probably get rid of the slack.