GPS Interference John Estes 10/18/1998 Hull #: 142 I finally got my problem solved. When we ordered our new C380, we ordered it with a Garmin 215 GPS with Differential built in. Well, the GPS worked fine but no differential. The dealer and the West Marine rep tried everything but still no workie. (I forgot to tell you I also had a inverter installed as well) By luck the rigger who was working on my boat turned off the inverter and lo and behold the differential started to work. So, after rewiring, trying a new GPS and new antennas, it was just interference from the inverter. So, I do not use the inverter when under way.