I bought half of the Livorsi GPS speedo kit. I could not spring for the hole set-up at the time but wanted to fill the dash up. My question is I already own a handheld Garmin gps unit. It has a data port on the back. Garmin sells a power data cable($30). Can I use my handheld gps as a antenna?(The livorsi antenna is well over $200!) If so what wires are used? The Garmin cable has a Positive,Negative,Data-in and Data-out. The Livorsi has a power,ground,lighting, and singal terminals.