🚀 go-pugleaf

It shouldn't be too hard to figure it out. Open your mouse and figure
out which of the pins on the connector is power and ground. Hopefully
you can do this by hooking one lead of your voltmeter (use a DMM with
a low current flow during the ohms tests to avoid blowing any chips)
to the pin in the upper left hand corner of one of the chips. That is
usually +5 volts. In the lower right hand corner is usually GND. If
you can figure it out apply power and then figure out what kind of
signal you are getting out. 
 
There are two possible problems with the output signal. One is that
the signal is inverted and the other is that it will not meet the
RSZ-232 specs. If it is inverted there may be some soldered-in jumpers
or something but you probably won't have this problem.
 
It is very likely however that the signal from your bus mouse will not
be RS-232. It will be a TTL signal. Though I haven't tried it myself,
it should be possible to prise out the appropriate 14XX chip in your
serial port card (assuming you bought one of those cards which has
sockets for these chips so you can buy it with one serial port and
them add another) and using wire jumpers feed the output of your mouse
directly into your UART. 
 
All this advice assumes there is some standard way of supplying power
to a mouse from a serial port. I must admit I have never looked into
it and so the matter is a mystery. Do IBMs put power on a pin? Does
the mouse fake it by drawing miniscule power from DTR? I don't know
but five minutes with a DMM should help you figure it out..
 
-cornhead