Amptron PM8400 is basically same board, here is it's "sheet" with the PS/2 pinout...if you check close the Amptron has exact same jumper and connector layout so assume the ps/2 part is accurate
You can check ground and +5v with a voltmeter to be sure.

Thank you so much! This is incredibly useful. I see from the label that the top left pin is number 1. So do the numbers work across? so top right is number 2? Then second row first pin would be 3 etc?

Look at "Pinout of the PS/2 mouse connector near the keyboard socket:" here: http://m571.com/m571/franczabkar/ps2mouse.htm

I think those PCChips s.7 boards use one and the same PS/2 mouse connector/header.

I think that m571.com pinout is wrong for the M537, in stu's picture pin 2 is clearly on right side of the connector, making pin 1 on left....
Also from the Amptron/PC Chips confidential board .pdf it lists PM8400 is the M537...the M571 is same as PM9100...

added: from TRW photo of back of M537, it looks like this-

Horun wrote on 2024-08-23, 21:16:

I think that m571.com pinout is wrong for the M537, in stu's picture pin 2 is clearly on right side of the connector, making pin 1 on left....

Nope, it is not wrong. You may compare the pin signals from the PDF according to signals positions on the ASCII "schematic". The only difference is in the way of pin numbering - bottom-t0p row pairs for PDF; linear numbering for ASCII.

Pinout of the PS/2 mouse connector near the keyboard socket (top side of the mobo):

1    1___2___3___4
2    |___x_______|   PS/2
3    5   |   7   8
4        |
5       key pin 6

pin 1 = ground
pin 2 = mouse data
pin 3 = not connected
pin 4 = +5VDC power
pin 5 = mouse clock
pin 6 = missing (key pin)
pin 7 = not connected
pin 8 = not connected

That does not easily answer

So do the numbers work across? so top right is number 2? Then second row first pin would be 3 etc?

properly where at least I tried by pictures.
So you are saying that if a different pin numbering "created by a user" is a good idea versus the pin numbering of production pdf and board silkscreen is a good thing ?
Does that not confuse things by numbering different than what actually exists when it is obvious that pin 2 is silkscreened on the board and the user created ascii calls it pin 1 ?
Ok whatever.....

Enough "talking".

PCChips/Hsin Tech "standard" PS/2 pinout is not standard for other brands s.7 boards. The very same is the situation with their C.O.A.St. modules pinout.