trouble shooting Garmin 176c > Standard AIS VHF, NMEA output problem

[pressuredrop]

ok here is the situation.

I Have a standard horizon GX2100 matrix ais vhf. this does not have an internal gps and requires GPS info from another source.

I have a garmin 176c gps. the garmin is too dated to display ais targets, however the VHF requires the NMEA output from the garmin for the AIS function to work.

I had everything connected (NMEA output of GPS to NMEA lowspeed input on ais) and working properly for about 2 months, and then all of a sudden there is no communication between the GPS and VHF, so no more AIS on the vhf...

I have redone all my connections and no change, and when I stick a light bulb tester on the nmea output wire, it does not light up. so I am thinking the problem is internal to GPS nmea output.

also, when the NMEA output on the GPS is turned on, I get a cyclically humming interference on my SSB (icom m700 pro). when I turn off the nmea out put there is no interference... note even with the output on there is no communication between the gps and Vhf.

anyone have any ideas for reestablishing the connection between the two? or assuming I am correct in that there is an internal GPS nmea problem, can anyone recommend a generic GPS antenna with NMEA wires that I can wire straight to the VHF?? that would keep the gps and vhf independent and I like that.

Thanks,
Ben