Making a monitor cable…

I have a project, to make 2 monitor cables. One 40 cm and the other 60 cm long. I have the male and female ends..15 pins. The problem is that I was given an 18 wire cable not 15…can it still be done? What colors go where, what colors can I leave un-saudered? Yes I have the sauder too.
Am I missing any details?