i just put this into my 07 vw gti, and there is no AM radio signal (i listen to AM mostly for news/sports/traffic reports). the was told that my car has 2 antennas... there is one on the roof out back, and another in the glass. the F90BT only has the one connection.
is there any way of getting the AM signal back? i have am reception when the stock deck was swapped back in.
I have an 07 Jetta with whip antenna (No shark fin) and don't get any AM stations either. I did the install myself and used the motorola to standard antenna adapter. FM is just fine, but no AM and I am about 100% sure that I do not have two different antennas in the car.
i'm not by any means knowledgable in this sort of installation, so i may have gotten the facts wrong.
the installer showed me the antenna wire from the car, and there were 2 connectors on it. he said one was for the whip antenna, and the other is for the imprinted antenna in the back window. the pioneer unit only had the one radio connector.
what is even more odd is that while the car was in his installation bay, it was still able to get a decent enough signal to be heard, albeit with some static. but once everything was buttoned up and i was sent on my way, the signal faded completely and i couldn't hear anything at all anymore.
i don't know what else i've missed 
It's called a diversity antenna. Rummage around in the RNS510 forum on VWNavi.com and you'll be able to find instructions on how to restore your AM using an adapter.
Likely issue is installer may not have used the proper antenna adapter. We use metra 40-EU55 which accepts a power antenna turn on trigger activating the vehicle's powered antenna. YOU DO NOT NEED BOTH ANTENNAS PLUGGED IN!!!
Other manufacturers make the same thing which work the same and you can find them on the internet I'm sure but I won't recommend or refer since I work in retail car audio and yes, it hurts us.
thanks... not trying to hurt anyone!
just came back from another installer. they used a metra equivalent as described above but... fm reception range improved, but no success with the am frequencies.... again, help? 
you could always go buy an antenna from the local auto shop, would save you one heck of a headache but might look tacky.
what do you mean by getting another antenna? as in replacing the oem roof-mounted whip antenna that's currently on the car now?
When you installed the power antenna amplifier adapter (Metra) where was the blue power wire coming from the adapter spliced?
what do you mean by getting another antenna? as in replacing the oem roof-mounted whip antenna that's currently on the car now?
the installer attached it to the radio output of the deck. It gives the antenna 12 volts once you have switched the radio on?
There's your problem... The power antenna lead from the Metra thing needs to be attached to the ACC lead. There is not enough power provided on the wire coming out of the deck to power the antenna amp. I had this very same problem in my 2008 Rabbit.
Its not the voltage that matter so much as the amperage getting to the signal amplifier. Amplifiers require a good amount of power as seen by the massively thick wires running to speaker amplifiers. That wire coming out of the deck only provides 500ma of power. (same as a usb port on a computer) Where the ACC lead will provide as much as the amp requires.
Getting another antenna would not solve the problem since
#1
I have no idea which antenna the wire that fits into the metra harness goes to. (even the wiring diagrams of the car don't really distinguish this)
#2
Even if the one plugged goes into the whip antenna it would still go through the antenna amp. If the antenna was replaced you would still get terrible AM reception. The only way to fix it would to be for you to rip apart the interior of your car and run your own wire to the deck. With the billions of airbags these cars have in the pillars, have fun with that one.
I have an 07 Jetta with whip antenna (No shark fin) and don't get any AM stations either. I did the install myself and used the motorola to standard antenna adapter. FM is just fine, but no AM and I am about 100% sure that I do not have two different antennas in the car.
You probably do have two antennas. After about 2006 (MkV's) most if not all VW's have what is called a diversity antenna system. The radio gets a signal from two antennas (hence the two wires) at slightly different positions on the car, usually the whip/stubby and the imprinted on the back window (sometimes it will be two antenna's imprinted on the back window if there is no whip). The radio will select whichever antenna has the better quality signal and use it switching between antennas whenever it deems necessary.
Some cars, mainly higher end (passat, tourag) and audi, will have a antenna "brain" usually mounted in the trunk or hatch that controls the diversity system instead of the radio. The advantage of these systems is that an aftermarket stereo can still take advantage of the diversity antenna system. Some of the lower end cars may also have this if they have the super new touchscreen NAV from VW <-- not entirely sure on that though.
The reason for this system is really complex and has to do with the phases of the incoming signal being slighty different at two different point and paths they take to get there. To sum it up its unlikely for both antennas to be blocked or suffer from attenuation at the same moment. so by having two antenna's your likelihood of having good reception is much higher.
hi... i just talked to the 2nd installer online and this was his response:
Here's the thing...the blue/white wire is not powering any factory or aftermarket amps. Its not connected to anything. So unless the amplified antenna requires a ridiculous amount of power to operate (which it does not as we have seen with amp'd antennas for the past 20 years) then I see no reason to move that wire to ACC.
Now, I can take it apart again and move the antenna wire to ACC but I sincerely doubt it would make any difference at all.
sorry for all the confusion... i'm just trapped between what he knows from experience and what is being said here... and i still have no am reception 
i just want to be sure of this because he has to charge me for time/labor evern time i go back.
I would just do it myself if I had the tools. So far after getting this radio I've opened my dash at least 10 times. Anyway take it for what you will but i was having the exact same problem in my 2008 Rabbit and this fixed it.
Also looking through the install manual on pioneers site for these units http://www.pioneerelectronics.com/StaticFiles/Manuals/Navigation/AVIC-F900BT_InstallationManual0520.pdf
I found something on the bottom right corner of page 6.
Be sure not to use this lead as the powersupply lead for the auto-antenna or anten-
na booster. Such connection could cause
excessive current drain and malfunction.
The above is copied straight from the manual.
If it is not an option for you to do this yourself I would show this to the install guy and make him fix it for free. This was his error not yours. You should not have to pay him to fix his own mistake.
The warning say not to use it as a POWER SUPPLY lead. Connecting the blue or blue white outputs of the f900 to the antenna trigger is not the same as supplying power to the antenna. The antenna amplifier has it's own source of power coming from another source in the car. The lead going through the antenna simply triggers it on much like the remote input of an amplifier.
The installer did not make a mistake.
the installer answered back to my email last night... here is what he commented:
Actually, now that I think of it, I would have connected it to the solid blue wire which is the antenna output. Makes sense since this is what we are supposed to do. The output however is the same for both the amp turn on and radio turn on so I don't see it making a difference.
i'm not very good at electrical work, and i don't want to mess with it on my own because i'm afraid that any damage i cause would affect the 2yr warranty on the unit. i have a tentative appointment scheduled for the upcoming saturday. i'm hoping to find good suggestions before then.
The warning say not to use it as a POWER SUPPLY lead. Connecting the blue or blue white outputs of the f900 to the antenna trigger is not the same as supplying power to the antenna. The antenna amplifier has it's own source of power coming from another source in the car. The lead going through the antenna simply triggers it on much like the remote input of an amplifier.
The installer did not make a mistake.
I'm looking at the wiring diagram right now... No it doesn't, power is supplied by the radio through the antenna lead. Do some research before posting...
Sorry gjas. Didn't mean to offend. I guess I figured my 18 years as a professional installer would qualify my response. Also w/ the R&D people at metra using a blue wire and saying to connect it to antenna output instead of red for accessory that they might know something too.
I guess since you've had to pull your dash apart ten times to make your stereo work makes you the expert. My bad.
please no fighting! we're all friends here... please? 
still no am reception until saturday....
Sorry gjas. Didn't mean to offend. I guess I figured my 18 years as a professional installer would qualify my response. Also w/ the R&D people at metra using a blue wire and saying to connect it to antenna output instead of red for accessory that they might know something too.
I guess since you've had to pull your dash apart ten times to make your stereo work makes you the expert. My bad.
What I get tired of is people thinking because something is done one way for most installs that it should be done that way for every install. (then not admitting they are wrong when it doesn't work) Some head units put out more power over the antenna wire than others. (Metra can't test for every eventuality) With my older Pioneer unit blue wire to blue wire worked fine but with the my F700 it did not. So I pulled out my Bentley CD for my Rabbit examined the wiring diagram and came to the conclusion that since there is no power wire running to the amp that the only way to get power was over the antenna lead. The Pioneer manual specifically states to not power an antenna amp with the blue wire.
If this installer would not just dismiss it off hand I wouldn't be so annoyed. If he used simple logic: AM worked before the radio was installed + AM doesn't work after the install = he messed something up and needs to fix it.
I'm sorry if I came off harsh its not what I ment. I just really really hate when people are wrong and won't own up. I know if im wrong about his I would apologize and do what I could to help.
Thumper: What state do you live in? If your near me I could help you out.
gjas, you can do the install yourself... get a harness and wire red to red, yellow to yellow, black to black, blue to blue... these are the most important to connect correctly (Once they are done you are 1/2 way there)
afterwards all you need to figure out is speakers...remember black strip is negative, no stripe is positive...
Blue stripe is remote, connect that (if needed) to antenna to give power.
As long as you connect yellow, black, red correctly... you will be ok.
Tools needed - Phillips, electrical tape, patience.
(there might be tools here and there you will need I cant be 100% sure, some cars need more work, some dont.)
Thumper: What state do you live in? If your near me I could help you out.
thanks for the generous offer, but i suspect we're not local (i'm from vancouver BC canada)
been to see the installer. he connected it to the ACC lead. now instead of either dead space or bursts of static, i get what i call "ghost whisperer" reception on my AM band... is this an improvement?
but things have now changed a bit. the strength/quality of both my AM/FM reception is being affected by the accessories in the car. i turn on the rear defogger and i get a faint buzzing sound. shift from D to R on my DSG transmission and the volume drops a notch.
is my car possessed?!?