Originally Posted by gearbox

here is a basic 04-05 wiring rundown.

each headlight bulb has a two wire connector. the lo beam is the easy one because the black wire on each side goes straight to a chassis ground. the power wire on the left side is red/yel and on the right side its red. these power wires connect to the headlight relays and get power when you turn on the headlight switch to lo beam mode. for the hi beam bulbs, they also have two wires red/blu and red/yel for the left, and red/blu and red for the right.

basically the lo beams are always grounded thru the black wire. so when you turn the headlight switch to LO, power comes thru the relays to the red/yel and red wires on each side and the lo beams turn on. when you switch to hi beams, the red/blu wires become a ground thru the headlight switch and cause the hi beam to turn on. its a much simpler setup than on the 01-03. basically no matter if the headlight switch is in lo or hi beam mode, ALL the red/yel and red wires going to the lo and hi beam bulbs will be hot. you can tap any one of these four wires to the new hid relay harness as a trigger. that way the new harness remains on in both lo and hi modes. i would personally tap the lo beam red or red/yel wire for the hid harness and leave the factory hi beam wiring alone so it works like normal to turn them on. im not sure if youve seen my wire harness i made for 01-03 hid lo beams with halogen hi beam, so here it is again. the only changes you need to make are instead of the H4 connector, you will have the lo beam 9006 connector and the trigger wire will be either red/yel (left headlight) or red (right headlight) from the 9006 plug. i recommend doing most of the harness on the passenger right side since its closer to the battery. you only need to tap the harness trigger wire to ONE power wire from the stock 9006 connector. so if you do it by the battery, it would be the red wire. if you buy a premade harness, it should have the trigger wire attached to a 9006 plug so you simply plug it into the right side 9006 oem connector. you can disregard the hi beam part of the diagram because your hi beams are already separated and working the way they are stock. if you have a bixenon projector, you simply tap the low volt solenoid shield wires of the projector (+ and -) to the stock hi beam 9005 connectors (red/yel and red blu for the left side headlight, and red and red/blu for the right side headlight). these wires must be "tapped/spliced" into the stock wiring because you still need to leave the 9005 connector and wiring intact and plugged into the 9005 bulbs so the halogen hi beams work.

Originally Posted by gearbox

just tap the projector solenoid (hi beam) to the stock honda hi beam wires. here is a pm i sent to someone regarding 04-05 civic wiring.