i'm gonna install my turbo timer soon~ should i do it with or without the harness? if without, will it do any harm to the car?

you're better off just getting a harness, it makes everything so much smoother to install. I mean, they're like $20 or $25 from fastwrx.com, you might as well.

get one....you will love yourself for it.

yes please get the harness, it just plugs into your stock harness for the most part although if you get one with all the goodies (tach, 0-60, etc) you'll still have to tap into you ECU harness.