Do your driving lamps work at all, or is it just the mod that doesn't work?
Basically, just double check your connections, make sure the connection is good. You're dealing with 2 wires, blue with red stripe (wire #1) and red with black stripe (wire #3). #3 is spliced into #1 coming from the back of the switch, and the other end of #3 that goes on into the dash is the one that get's taped up. Of course make sure that the other end of #1 is connected back up to the splice you just made coming from the switch. Basically you're fooling the driving lamp relay into thinking the headlights are on by replacing the headlamp power wire with the parking lamp power wire, which of course becomes live when the parking lamps are turned on.
Double check your connections, make sure they're correct and that you have a good connection. The mod should work provided the right wires are connected...I really can't see any way that it couldn't work, unless the lamps aren't working at all.