T5 2012 Aftermarket radio antenna power.

[Bob Bob]

Hi there


I note a lot of discussion about aftermarket radio etc problems to do with CANBUS. I do however only have a simple question.


Is the mirror preamp (antenna) power only activated by placing 12V on the coax inner (via a suitable adapter), or is there a CANBUS relay somewhere that is turned on when the processor sees that the radio is on?


Am trying to ascertain if the preamp in the mirror is blown. (Haven't been game to try prying the thing apart)


TIA Bob

[Sunny43.5]

I might ask do you still have the factory radio fitted or has it been changed , seems that if you remove the factory unit the aerial will not work correctly . Now this is what I was told by a large car radio fitting place in Brisbane , you use a test light connected to 12V tune into a weak station then probe the wires on the connector on the back of the unit from what the guy told me when you hit the correct one the radio will suddenly work again . Now I cannot vouch for it working as I tried it with ours and didnt seem to work so I ended up fitting a roof mount antennae which you may have seen on another post .

[Bob Bob]

Its actually a bit more complex than that. Have a Kenwood unit running off a large Lithium aux battery. (camper van) The only use that was made of the existing connector was for speaker wires.


You are suggesting a separately powered amp under the dash? Pretty sure it has an active antenna (with amplifier) in the left mirror. I haven't been game to pull it apart to check though! I (hope I) validated all the wires/pins and I didn't see a Vout from the unit.

I don't have any more roof space for another antenna (have 5 already), but was thinking of making a metal tape dipole inside the windscreen.


Tnxs. Good to know..

[Sunny43.5]

That makes sense because if you are only using the speaker wires the factory wiring would be looking for a signal from the head unit itself . Like an amplifier for a stereo it needs a signal from the head unit to turn it on it's called a Pcon wire . So like I said maybe one of the unused wires would be triggered by a power source from the original head unit .Also worth noting a lot of the signals from the head unit would not even show up unless its plugged in . I found this out recently when fitting a couple of the those VW Logo downlights to the bottom of the the door trims , using a volt meter to check for connections at the interior light drew a blank whilst the light was on a 12 volt signal could be read but if you looked with continuity for an earth signal NOTHING really bizzare . But when the new wires were connected it works !!

[Bob Bob]

Doing some web browsing I found there are a lot of different VW setups. My original OEM radio/CD was about the cheapest one available with only front speakers and no audio amplifier. The connector that would take such an amp control signal though only has 5 pins. (I took photos etc) They are CAN+ and CAN-, ground and +V. The last pin is the "safe" anti-theft encoding pin. The initial installer insisted that 12V had to go along the coax centre and supplied one of those common adapters. The unit worked okay in the strong signal area, but is useless outside of that.
I then found a photo of an after-market mirror antenna that plainly showed a coax and two other wires going into it. To me that meant either the extra wires were CANBUS or direct power. I also noted that some VW diagnostics show whether the antenna power is off or on. That kind of implies the antenna has a CANBUS node thing or there is a CANBUS relay elsewhere that uses those two wires to only supply power. Hence my original question.

Apologies for explain this in length. In hindsight I probably should have used a CANBUS adapter from some place like Aerpro, but I an still not sure how it is configured..
Lack of lighting ground can be as simple as one side being tied to +12 and the other side switching to ground. ie the ground not +12v side is switched.

I have taken the door trim off once. If I take it off again I might check that the 12V is present at the coax centre there. That will kind of disprove that there is anything but a plain cable from there to the radio.