The RS232 cable was attached to the TomTom and all works fine with the serial interface. I also attached the suspected audio line out to pin 1 on the cable and the line input to pin 2 in case they prove useful in the future. They are normally RTS/CTS on the PmodRS232 board but it has removable jumpers that will provide convenient access to the lines.
Telemetry2U IoT Docker Projects
Telemetry2U IoT Microsoft Profile
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List of IOT / LoRaWAN companies
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