Welcome to TM Bilymog. The M3W speedometer is not the same as the 4 wheel Morgans item, at least entering the calibration mode is different. It sounds like your speedometer has gone into the calibration mode with the messages of INPUT and FREQ, this is usually done by shorting two wires together at a plug in the loom but either your speedometer is faulty and done this on its own or the wires have shorted somehow.
There is a set of instructions about calibrating the speedometer on the Morgan Three Wheeler Club website
https://www.mtwc.co.uk/news-post/. They are available to members and were published in December 2019 . If you cannot access them PM me with your email address and I will send them to you. If you know how the system should work this may help with your diagnosis.
