Originally Posted by bostongmw
well I installed the lights without the relay to see how they work ... WOW.
simply blows away the crappy KC kit I initially purchased.
still not sure how much difference the relay makes and if its worth the hassle.
Without seeing a schematic of the wiring harness I can only suspect the reason for the relays, but as an electrical engineer if I am correct you should definitely use them.
If the new lights draw more current, meaning use more power, than the old lights, the stock wiring may not be a large enough gauge to handle the increased load without overheating. And over heating of wires can lead to the insulation melting and the wires shorting out or even catching on fire.
And if the additional power requirement is true and you just replace the wiring from the light switch to the new lights, you just move the problem to the light switch and the wires feeding that switch. Which could cause your light switch to fail prematurely since it will be switching more current than it was designed to handle. Or worse, if the wires feeding the light switch are under sized they could over heat and fail as mentioned above.
If the new wiring harness has new wires running from the relays to the new lights one of the things mentioned above is most likely true and you definitly want to use them. The relays purpose is to use very little power from the factory light switch to the relays to turn the relays on, which will then turn on the more powerful lights, using the relays larger contacts that are indeed designed to handle the additional current load.
Again this is all speculation since I have not seen the schematic for the new wiring harness or the wiring diagram for the JKs lighting circuit.