It appears you are receiving GPS and other NMEA data on one COM port and only AIS data from the AIS250 on the other. If I am correct OpenCPN should tell you which one is the GPS/NMEA port by indicating a GPS active when you configure the correct port in the GPS tab of the Toolbox window. The other port should be the one from the AIS250. The first step should be to sort out which port is which, if you haven't already done so.
You can monitor
the NMEA traffic on the GPS port by clicking on the "Show GPS/NMEA Data Stream Window" checkbox in the GPS tab of the OpenCPN toolbox.
AFAICT OpenCPN provides a data stream monitor
only for the port designated for the GPS. Once you have sorted out which ports are which you can monitor the AIS traffic (if any) by temporarily setting the GPS port as shared with the AIS port.
It does appear the problem is in the cable that was made up and connects to the USB adapter. I assume the tech who made it up just cut off the male end of the cable and picked the red and black wires from the 9 or 10 wires in the cable. Those cable colors don't conform to the pinout I provided in an earlier post. However, there does not appear to be a standard color coding for RS232
cables, except maybe for a single manufacturer. You can test the cable with a multimeterr for continuity between the cables connected to the AIS250 and the pins on the female end of the cable which connects to the USB adapter.
You should get continuity between the red cable and the RD pin in my diagram and continuity between the black cable and the SG pin in my diagram. If not, test the other wires (hopefully the tech didn't cut them off flush, just taped them to the outside of the cable. Otherwise you will have to strip off more of the cable jacket.
You may not be able to directly test the continuity at the female terminal as the probes on most multimeters are too thick to go into the pin sockets. You may need to insert a brad or needle into the sockets to get a good contact.
Hopefully it is a problem with the cable and you can find the correct wires and start receiving AIS in OpenCPN. If the cable tests good, but still no AIS then the culprit may be the USB adapter. They are cheap
, try another make.