These are all very good suggestions for the OP. Other than that, I'll pitch in another method. Make sure the cable are not criss crossed. and the stranded metal wires aren't touching at the back of the DB25 connector. Like when i removed the older wires from the DB25 conn i used from an old IOMEGA zip drive cable. I unsoldered all the old wiring to the pins at the back of the conn, but there was some stranded wire stil stuck to the ends of the pins I wasn't using.
So, long story, short, the wires I would eventually solder on the back of the connectors, would accidentally touch one or more of my wires. If you notice that there are many wires for a parallel port connector, then you'll realize how uncombersome it is to stick a desoldering braid in between each pin. So, just be careful. I just bent the strands away with a fine eyeglass screwdriver.
But , now I use USB nand flashers.