Perfect! I wired up a plug to suit the above pin out and it's working beautifully. Thanks very much!

Bit of a long shot, but I thought it was worth a shot. After spending more time than I'd like to admit trying to get 4 seperate serial mice to work with this motherboard, I've given up on serial and now need to attempt to connect a PS/2 mouse to this old hardware. https://theretroweb.com/ …