I am working with a friend who has an 02 38 topgun. The GPS speedo stopped working last season when the GarminGPS crapped out. The Garmin has been replaced and seems to work fine, but no movement on the GPS speedo. Assuming everything is hooked up correctly, what is a possible cause for this? I have read posts about an antenna battery or maybe the Garmin needing to be setup thru the menu options. any info will be helpful. thx

you have to go in the menu and turn on the NMEA signal

Thanks BoatNT. I did that today. There were 2 options for the setting; 1 for high speed and 1 for standard, I played around with these while the boat was on its lift. I found the needle either jumped to 30 with 1 combination of settings, floated between 0 and 10 with another setting, and finally just sat at 0. I hope this has remedied the situation. The Garmin has an internal antenna, but is wired to the antenna on the boat. The Livorsi GPS speedo is wired to the Garmin. If the problem still occurs, does this antenna battery exist? and, should it be replaced? Thanks.

I have both a gaffrig and an autometer gps speedos hooked up to my garmin. The autometer will accept either NMEA 0183 or NMEA high speed. The Gaffrig won't take the High Speed protocol. Use the regular NMEA to be on the safe side.