good small cheap compatible computer?

You mean with the PC shutdown, measure the voltage between GND and Pin12 directly on the cable ?

No, I mean with the PC on and linuxcnc running, operate the Z limit switch by hand
while measuring the voltage at pin 12 of the parallel port relative to ground in both switch states.
(you may need to access pin 12 on the back of the breakout board)

Ok i tried reading directly on the cable with no PC connected before I saw your latests post

When the switch is off I read +4.97V
When the switch is on I read +0,07V

Tried a few times on/off and got consistant readings...

Will see if I can reach pin 12 on the breakout board.

Also as stated on the other thread, everything works perfectly with an old PC, the problem is only seen on this new Q1900M PC