It's my understanding that it's just a ground wire and will work if you have it grounded for testing purposes. Or, do what I did... still have the wire connected to the parking brake but have a switch to bypass so that you can override it. Mine is installed on the passenger side so the wife can override and have full access to the GPS while I am driving.

I have the same GPS unit but using the XXV-05V DVD reciever and must say that the KNA-G510 was somewhat of a disappointment compared to Garmin's portable units. Perhaps they will release a firmware update to speed up the unit (drawing map data) and accuracy. Sometimes I would be exiting a highway or road, and it still thinks I'm on the original route until 30 secs later or take 10+ secs to tell me that I've gone the wrong way. The voice guidance is not as accurate too and would tell you to turn way too late. I have the latest firmware uploaded and Kenwood/Garmin have not address these issues yet.