Prostreet144

I have searched and still no answer. Since I purchased the boat the gaffrig speedometer has not worked so I'm a little lost. Gauge has a tattle tale switch, everything is wired correctly. No antenna but it is wired into a garmin gps546s, I have tried both nmea outputs from the gps to the gauge (blue wire and gray wire ) and I get the same results with the speedometer running through its start up procedures and settling at 9 mph ( not 9 o'clock position like most failed antennas) I know the baud rate is suppose to be 4800 from searching but I do not have that option in the gps setup, I can choose nme standard and high speed. With the gps in sim mode at 50 mph ,standard stays at 9 mph (7 o clock) and high speed reads 0 mph ( 6 o clock). So I have either incompatiable devices, a bad gps with 2 bad out puts( unlikely) or a bad gauge? Any suggestions??