There is no standard for PS/2 to serial adapters. Every manufacturer that made backwards compatible mouses had their own different pinout. If you can't find the one that came with the mouse you might be out of luck unless you just keep buying them randomly and get lucky

I had a go at working out the wiring for a MS 45717 PS/2 mouse, which is also serial port compatible: Re: Microsoft PS/2 to serial pinout?

But there's no guarantee that Microsoft used the same pinout for different mice.

Perhaps instead of adapting the mouse to serial, you can mod the motherboard for ps/2?

Native PS/2 mouse implementation for 386/486 boards using the keyboard controller

Look for a Microsoft branded adapter, If I had to guess the correct one for that mouse is labeled "68666" (just a guess due to the cable matching the color of these particular adapters). But keep in mind that there are differences even between Microsoft's own adapters. I have a MS Basic Mouse from the late '90s and it only works with the adapter that came in the box, a couple of older MS branded adapters I have do not work at all.

Thanks all - I'd assumed it was a standard, makes sense it's more a workaround at the manufacturer level. I thought it was a little weird they gave the pinout for the adapter on the item listing, but now I'm seeing at least a few other pinouts

The 68666 adapter does seem like it maybe it, I see one for sale for cheap so picking it up, will see if it works and note the pinout I find here. Otherwise I'll try wiring up my own adapter

Not sure it applies to these, but a thing to be aware of is some multi mode mice need to have a button held down at power up to switch modes.

To follow-up, got my 68666 adapter and it didn't work, it does look like they were made for each other , same color, line and dot design

Here is the pinout I was able to come up with, it doesn't quite seem to match the ones from Snufkin

PS/2 Serial
6 NC --> 3 RXD
4 +5V --> 7 CTS
2 NC --> 2 TXD
1 DATA not connected
3 GND --> 5 GND
5 CLK --> 4 DTR + 6 DSR

I did open it up and got a pic, I see some saying it could be four internal wires, some 6, and possibly there are two adapters with same part number. Will keep messing with it

On the adapter you got, it looks like the TX/RX/GND match and it's the +/- 12V and reset signals that are different. The colours of your internal 6 pin connector match the one that was in my mouse, and the PCB revision is the same.

Some of the resistors are different values and the PIC chip is slightly different: mine is /P308, yours is /P304, so I guess mine has a slightly later firmware, which might change how it handles the signalling.

Even with those differences, it might be worth having a go with the wiring that worked for mine.

Did you ever get an adapter working? I have the same mouse and snufkin's wiring as well as the documented wiring for the 68666 adapter in the same thread don't work.

Yes, in the end I got a working adapter for it. I bought another mouse that claimed to be NOS, however when I got it it was dirty and I don't even believe even serial compatible. However, it did come with a sealed I assume generic adapter, I'll include a pic anyway, which did work on my original MS Serial-Mouse Port 2.0 mouse. Checking the pinout it's:

PS/2 : DB9
1 not connected to DB9
2 > 2
3 > 5
4 > 7
5 not connected to DB9
6 > 3

these are connected together on same end:

DB9
4 + 6

PS/2
5 + 1

PS/2: pin 1 lower right looking into female connector
DB9: pin 1 upper right looking into female connector

Thank you. Unfortunately that didn't work for me either. I'm assuming I'm doing something wrong or there's some other wonkiness going on here. I'll have to spend some more time with it when I get a chance.

I did another check and realized 4+6 are tied together on the DB9 and 5+1 on the PS/2 as well:

PS/2 : DB9
1 not connected to DB9
2 > 2
3 > 5
4 > 7
5 not connected to DB9
6 > 3

these are connected together on same end:

DB9
4 + 6

PS/2
5 + 1

PS/2: pin 1 lower right looking into female connector
DB9: pin 1 upper right looking into female connector