Bought a 'spare' STM1 mouse on a whim, it was lowball ebay win so why not.
Turns out it doesn't work
Mouse port is fine as my usual STM1 and Speedmouse both work.
Symptoms: If I turn the STE on with the mouse connected, I get a repeating keyclick noise. When the STE boots up there is no pointer. Wiggled the connector/cable and it seemed to briefly display the pointer which whizzed straight off the screen (once or twice) but mostly there is nothing, no pointer, no selection box.
Are there any things I can do to get it working? Or just throw it in the bin as a dead loss.