I first cut the end of my parallel port cable that connects to the printer, stripped back the insulation to expose the wires.
Then you strip the wires back, and 1 by 1 with your voltmeter, check for continuity for each wire to each pin on the male parallel port connector. Using an alligator clip on one of your multimeter leads makes it a lot easier to test the wires. Make sure to write down the color of wire for each pin. ( I haven't found a standard code for parallel port cables), and also the Belkin parallel port cable I used had more than 25 wires, with several of the wires going to the same pins... Anyway, here is the color code I found, but I'm sure yours will be different unless you are using the exact same cable:
// Pinouts for the Belkin Parallel port cable. Multiple wires go to the same pin on some wires..
// Also, a lot of the secondary colors are terribly hard to read (ie: black/gray/brown) double
// check your connections.
12. Blue & Red/Gray
13. Blue/Black & Red/Gray
22. Green/Black(gray?) & Yellow/Gray
23. Pink/Brown & Red/Gray
24. Green/Black(gray?) & Blue/Brown & Violet/Brown
25. Pink/Black(gray?) & Gray/White & White/BlackOptional
If you have a breadboard and want to test this out before soldering it all together, you should note the pinouts for your Serial DB9 cable as well. There is no standard here either, but one of the cables followed the resistor color code. My other one did not. To connect these up to a breadboard I had to cut small pieces of CAT5 and solder them to each wire... not exactly fun, but worth it to me since I wanted to see this work before I started soldering.
You will also want to download PPJoy now, and see if this works for you: http://ppjoy.bossstation.dnsalias.org/
(I use this version in Windows XP)
Another link for a newer version of PPJoy is here:http://ppjoy.blogspot.com/2009/11/finally-new-version.html
(possibly works better for Windows 7/Vista)
Install it, Add a Joystick from the new PPJoy item in your control panel, and make sure to use the NTPad XP drivers. After adding, I had to click the mapping button, which gave me an error, hit cancel, then Windows recognized the driver and I was able to see it under my Control Panel / Gamepads item. This let me test all the buttons out. If all the buttons don't seem to be working, you may want to check in your BIOS settings to make sure your Parallel port is set up to ECP or EPP mode. If you have an older computer you may not have this option, or the parallel port may not be compatible, you can try a different schematic / driver in PPJoy. There are several different ones you can use, but I chose this one because it allowed for 2 ports and the least amount of other parts (diodes, etc.).