I bought the power harness for my headlamps and didn't buy them 4 my fogs. Both seem to work just fine although I would air on the side of caution and say get them. I believe they are only $15 more and I think you should have a solid 13.5v going to your ballast's and not have to worries about burning up the wires on the standard harness. NO need for the error eliminator.PLEASE READ THIS PART!!! A lot of people on this forum hates the high/low functionality of certain HID bulbs. I bought the headlamp bulbs with the high/low functionality and am glad I did. It isn't the best output on high beam but it DOES MAKE A DIFFERENCE and out in the country, I'm glad I had it. Also, on the color temperature, i have 6k for both fogs and headlamps. Solid White. Just the way I wanted it. Let me know if you have any more questions about DDM, the bulbs, or the installation!