I did mine a bit differently...
I ran the cables through the hinge gap in the windshield same as you, but instead of bringing them in to the cap, I used the hole through which the wiper motor comes out of, and went directly behind the dash. On the passanger side, I made a hole just big enough to pass the wires in the same way. From there, I also used the ruber plug, and connected o the battery.
Since I do not have any rear wiper, I used the speace where such a switch would have been mounted, but I did tie in the lights to my brights (I figured I would most likely have the brights on anyway when I use them) using the supplied relay.
I am happy to say that my lights are working great, and that the are VERY bright; they were not joking when they called these lights DAYLIGHTERS! I will not be using them for on-road, as any oncoming driver would be blinded at a very respectable distance... But they work GREAT for offroading!
Felipe