Hondata

Hey. I just got my first honda and its a 04 civic. Its great. Anyway i just installed a faze tach and when idle it reads me at 5 rpm. For some reason its reading the wrong RPM but when i give it gas it goes up. I heard i might need a filter. Anyone got any ideas? Also anyone know which wire is the dimmer? I really dont want to pull the radio out. PLEASE!!! Diagrams anything please!

Ok found out why. It had to be closer to the engine. So i had to run it thru the firewall. Kinda wierd but works now. I just need to know where the dimmer is i tapped into about 30 wires cant find anyone know where the dimmer is on a 04 civic? I rather not take the top dash out and radio tryin to avoid this please help....