I'm in the process of installing a Delphi SkyFi unit in my '02 SC430. Mounting the antenna under any metallic object won't work. The signal won't penetrate through metal and the antenna is directional - aims up, not down.
After some experimenting on a road trip today, I found the following:
1. It works great when mounted on the small roof section above the rear view mirrors. I antenna wire is so small that the top will close with no problem. I routed the wire behind the weather seal and down under the dash.
- Reception was perfect, but the small magnetic mount antenna causes a fair amount of wind noise above 70mph. It looks pretty good, but the whistling makes this mounting location a non-starter.
2. Moved the antenna to the dashboard. I wedged it between the windshield and dash, directly under the nav system in-windshield antenna. It worked pretty well in that location, but I found that reception will vary based on the direction the antenna faces. The best results were found when it was positioned with the wire (rear) side pointing toward the either side instead of to the front or back of the car. In that position, I had no drop outs whatsoever. Obviously results will vary based on the terrain. I live in the Atlanta, GA area which is a fairly hilly area. If you're in a flat area, this position will work just fine and isn't visible from the outside.
I'm still looking for some good options for mounting the unit inside, but so far nothing look good. It's a damn shame that Lexus/Mark Levinson hasn't produced a clean interface method into the head unit. FM modulators can't match the dynamic range and signal response of a hardwired audio interface. The tape adaptors are a little better, but have create a real eye sore...