I distilled 3 years of posts and debates and put the BEST version here. For instance, you can put the GPS antenna lots of places, but where I tell you to put it is where it gets the best reception according to Ron Stygar's Antenna Placement Test. (See the FAQ.) Feel free to peruse the other information on the Users Pages and use what suits you. Please let us know if you find something we missed.

The best and fastest install instructions are from Mpire and his 4773:

Unscrew the old head unit.
Pull out.
Pry connector off.
Pull out TP
Snap on adapter etc.
Screw on guide pin.
Pop off center vents
Stick antenna on top of center air vent inside dash. (perfect spot right there for it.
Slide in TP, stick hand through air vent hole to line up pin in back
Push TP in all the way.
Snap center vent back on.
Turn on.

That's what Traffic Pro in a Z3 (and all cars) was MEANT to be- but Mpire had a cable that already had the GAL wire attached- and that is really the only thing we're missing.

First, a few basic points- like WHAT are you installing?