The XP1541 and XP1571 parallel cables
You should follow these instructions if your drive has no parallel capabilities yet and you want to create a parallel port on your drive and then connect the cable to it. This is the preferred method because you can also make use of it with a Commodore machine.
You need the following parts to build this cable:
Step 1. Solder one end of the cable onto the game plug.
Step 2. Solder the other end of the cable onto the parallel plug. You should have the following connections:
You can find the description of all parts used on the diagrams at the legend page.
Source: The Joe Forster-STA homepage