I need to know where i can hook up the orange and white wire on my harness in my 2000 323ci so that my navigation dims when i turn my lights on at night.

Just off the top of my head, there's usually an illumination wire behind bmw radios. So you could just tap it onto that. Don't remember the wire color.

buy the harness from european autosource or ebay. that's a lot easier

You don't necessarily have to go to the vehicle's ILL wire, just any source that throws a positive when the parking lights and/or headlights are turned on. When that wire senses a positive is when it dims. Hope that makes it easier for you