The factory 9003 harness that we have has 3 prongs. This is because the 9003 bulb has two filaments, unlike most bulbs. One blade/wire is the ground, the other blade/wire is the power to the low beam filament, and the third blade/wire is the power to the high beam filament.
The reason this presents a huge problem is this: What the headlight switch does, when activated, is kill power to the high beam blade, and send power to the low beam blade. This turns on your low beams. When the highs are activated, it kills power to the low beam blade, and sends power to the high beam blade, turning on the high beam.
The harness that came with the headlights converts from 9003 to H7 by allowing you to plug the 3 blade factory harness into a 3 blade receiver on the headlight harness. Inside the projector dust cap is an H7 two blade female receiver/socket. Here is where the major f-up comes. The new FK headlight uses a moving shield to switch between low beam and high beam. They attempted to wire this correctly, and actually did, with the harness that came with the headlights. But it only works if you have a two blade system coming in (which we mimicked with the switch box). The 9003 harness is constantly killing power to one of the two filaments in the bulb, in order to operate the other, so what is happening by the time that signal gets to the H7 bulb receiver is that it never has enough power, nor a proper ground. This is why it worked when we hooked the harness into the switch box. When we did that it was a getting a clean fully powered, and properly grounded signal for each switch. They headlight appears to be wired correctly, but for the wrong type of system. I would be amazed if these worked for anyone with a Mazda 2 that uses a 9003 system.
He did a little bit of handy splicing for me (totally reversible) and everything works now as it should. Im really happy with these, but I would not recommend them to anyone who is uncomfortable with a little wiring modification.
