Garmin GPS hook up to new GPS speedo?
 

Has anyone ever heard of replacing the old pitot tube type speedometer with a new Gaffrig GPS speedometer and using the separate GPS map as a signal receiver instead of buying a new antenna-satellite receiver for the speedometer? I have a Garmin 172 c. Is this possible with a special connector?

Yes, I just did this. I added a Gaffrig digital speedo on the passenger side that is fed by the ouput from my Garmin 540. Your Garmin 172c has the required NMEA outputs as well. Just connect either the blue or green wire from your GPS to the input for the speedo. It's important to ground the speedo in the exact same location as the GPS, too. You also need to make sure the NMEA is configured in your GPS. It's all in the manual.

Thanks for the info. That is nice to know and it will save me some money. Thankyou!