Kelly sends harnesss to plug into the factory harness. I'm sure it works with whatever he's selling. My harness was hacked to shlitz by the chromosome missing previous owner, so I didn't use them.
its probably a similar light to what I have in my 40, and that doesn't need a relay kit.
I'm pretty sure I tried it without the relays, but I don't remember for certain. My buddy and I used the same relay kit in his 82 Hilux. I don't remember how that went down, but there was some ****ery afoot to make that work there too. Plugging in whatever 5x7 light he bought, it didn't work just plugging it in.
If your rig isn't hacked to bits like mine is, it's probably not a big deal. Even then, the relay kit wasn't difficult, just required patience to work through the 24 possible permutations when you pull three wires from the available four.
Hindsight... I'd make a list, and just work through the list if you do. I didn't do it systematically, and I leaned on pure autism to make it work.

I tried to logic my way through first, but I'm far too stupid to rely on that.
ABC
ABD
ACB
ACD
ADB
ADC
BAC
BAD
BCD
BCA
BDA
BDC
etcetera
It's not hard, just a pain in the ass