Well, after losing my mind looking at confusing or unlabeled pinout images online, I decided to crack open my mouse to verify the pinout myself.

Most of the confusion was generated by the Bus mouse wikipedia page which I have updated myself this evening. I also updated the pinout image on the wiki page with numbering since the old one had no numbers (the pinout was technically correct but the order the pins were counted was different than any other DIN numbering online and was not explained).

https://en.wikipedia.org/wiki/Bus_mouse

If the information on the wikipedia page does not match what is in this post at some point in the future, then it has been changed again for some reason. Trust whichever one you want... 🤣

The mouse I used to test this is labeled "400 DPI BUS MOUSE" Model No. TX-2B-HR . It came with an ATi VGA Wonder card that I picked up a while ago, and I believe it is the original mouse that came with that card. I also got the box from the seller and it says that the card includes a "Microsoft compatible bus mouse and mouse port".

Most importantly, here is the pin numbering I used. Most other DIN pinouts that I found were done this way, so I stuck to that:

Female port pin layout from the front.

Pin 1 - +5V - Vcc
Pin 2 - XA - X position
Pin 3 - XB - X position
Pin 4 - YA - Y position
Pin 5 - YB - Y position
Pin 6 - SW1 - Button 1 (Left)
Pin 7 - SW2 - Button 2 (Middle)
Pin 8 - SW3 - Button 3 (Right)
Pin 9 - GND - Ground

Here is the mouse I used to test it:

The headers inside the mouse that I used to identify each pin (continuity test from header to male end of cable)

And the little scribbly drawing I made while testing the male pinout based on the header markings (obviously pin order was flipped for female diagram above):

After doing all of this manual testing I finally stumbled upon this page on MinusZeroDegrees which has the correct pinout and also explains the weird numbering that was previously on the wikipedia article:
https://www.minuszerodegrees.net/msmouse/Micr … oft%20mouse.htm
So, as usual, that site is an excellent source of information. Still, it's probably not a bad idea to back it up with a physical hardware test like I've done here.

Anyway, I hope this saves people some time and prevents some burnt mice\interfaces in the future. There aren't many of these things left! 😮