Connecting the monitor on/off circuit.

You may want the ability to turn your monitor on or off through software. (I actually don’t use this feature, but it may be handy.) In order to do this, you need to use the low level signal from the parallel port to switch the AC line to your monitor, taking care to isolate the AC power from the logic circuit. 

There happens to be a device designed to do just that - an SSR (solid state relay). Same function as a magnetic relay, but entirely solid state, and the logic signal is opto-isolated from the load. (Meaning if the power supply in your monitor detonates, it wont fry your PC via the printer port.) Here is one from DigiKey that should work at a cost of $3.53. It’s rated to handle 2A at 120V AC, so check the power requirements of your monitor. 

To use this SSR, connect Pin 3 of the SSR to pin 6 on the LPT port. Connect Pin 4 of the SSR to any ground pin 18-25 on the LPT port. Cut the hot wire to your monitor, (obviously while it’s disconnected) and connect one end of the cut to pin 1 of the SSR, and the other end of the cut to pin 2 of the SSR. 

Cheesy mspaint wiring diagram here