i just recently purchased a set of bmw 540 projectors and i own a 96 civic ex..now obviously the plug from the ballast doesnt match the plug from my harness..i know i can just splice the wires but the civic headlight plug has 3 wires and the bmw only has 2..i know 1 is +, 1 is -, but wut is the other wire for??
(hope u understood)

 

no one knows??

 

what kind of ballast are they? Sounds like hella gen4. you'll get a better answer if you search hidplanet.com/forums/

 

3 wires, 1 for low beam, 1 for high beam, and 1 for ground. I would try and splice each one see which result you like the best. I would assume the BMW probably had two separate housings for high and low beam thus the reason there is one 2 wires whereas the civic has 3 because of integrated high and low beams.