I'm having the same problem with an MCR12 PS/2 version talking to an Arduino Uno. My cabling is as suggested above.
Scanner pin 1 (brown) to Uno Gnd (black)
Scanner pin 2 (red) to Uno +5V (red)
Scanner pin 7 (yellow) to Uno Data (pin 4) (yellow)
Scanner pin 8 (white) to Uno Clock (pin 3) (white)
I'm using version 2.4 of the PS/2 keyboard library, with the sample sketch modified with IRQpin 3 and the DataPin from 4.
Apart from the IRQ pin placement, my setup is identical to the photo above.
I'm only getting "Keyboard Test:" as output, and keyboard.available() never returns true.
I've tried the scanner defaults, and other 9600/Keyboard/all codes combos.
(EDIT: Updated wiring and attached photo)
[EDIT] I just read at http://www.jkmicro.com/ps2keyboard_en.pdf which suggests CLK and DATA need pull up resistors?
"DATA and CLOCK signals are “open
collector” type: they need to be “pulled-up” to
5VDC via 10kOhm resistors. Remember that
a logical “0” generates a 5V signal, while a
logical “1” is observed as 0V !"
It seemed like people had this working without them from the posts above?