IF IT WERE ME....I would make my own without a relay. I'll get shit for saying that and I'm not recommending it by any means. But there is no reason for a relay on an LED bar as long as your wiring and switch are worth a damn. It just makes it simpler to wire/install for me is all.
That being said, I think with a new harness you can make it work as long as it's wired properly. The relay is the confusing part for most, myself included. I'm hoping someone else chimes in that is familiar with the relay part of the harness.