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Replacing PCM 3.1 with standalone Bluetooth receiver


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Hi all,

I'm in the midst of planning a bit of an unconventional PCM replacement and wanted to see if I might be able to get some feedback on a few questions that have popped up as I've gotten along in the process.

Long story short, the PCM 3.1 in my 981 GT4 has been replaced twice now due to the prior units essentially going into an endless reboot cycle. And before you ask, it's not the XM problem—the PCM doesn't even power on long enough to be functional, essentially like the PCM in this 991. 

I'm now on the 3rd unit and am pretty much done with Porsche OEM head units; the latest replacement in there now was installed last week and works fine, but I consider it a ticking time bomb given past experience and am planning on simply uninstalling it preemptively and replacing it with a Bluetooth receiver that connects directly to the speaker system (the Out of Sight Mark 4 Bluetooth receiver, to be more precise). My reasoning for this is that nearly all of my music & nav audio is driven off of my phone at this point, so a head unit is really just a conduit to connect my phone to the audio system—I derive virtually no function from the head unit itself. (I also acknowledge that jslo73's HDD to SSD swap from RL/P9 would possibly be a solution, but I'm already past the point of even wanting to use the PCM full stop)

Here's a list of parts / equipment that I've purchased / am in the process of purchasing for this little project:

 


Broad strokes, I think the Out of Sight unit should be pretty plug and play, but I had a few questions that I was hoping folks here might be able to help with.

 

  1. What circuit(s) is the 12V radio power connected to? – I'm going to test with a multimeter once I have everything apart, but in terms of the power output coming from the Quad Lock connector, is it strictly on the Ignition/Run circuit? I ask because I notice that with the harness adapter wiring diagram it calls for you to plug in an accessory signal line into an empty fuse; however—given that the OEM head unit doesn't have this signal wire—I'm wondering if the 12V line coming from the Quad Lock is hooked up to both the Accessory and the Ignition/Run circuits.
  2. What wire(s) is the integrated hands-free microphone hooked up to? – Given the Out of Sight unit has a mic input, I'd love to make use of the preexisting hands-free mic in the steering column, but haven't been able to find any info regarding how exactly it's wired up to the PCM in the first place. Anyone have any info on this? I'm operating under the assumption that I'd be able to splice the wires to a 3.5mm TRRS microphone jack which I could then plug into the Out of Sight, so I'm crossing my fingers the integrated mic isn't wired up in some kind of exotic fashion.
  3. Glovebox USB / AUX input—how are these powered? – When my last PCM died I was puzzled when the USB port in my glovebox no longer worked, but then the tech at the dealership clued me in on the fact that the glovebox USB / AUX connections are powered from the PCM itself, so it'd make sense that when the latter no longer works, neither will the former. AUX is essentially going to be useless in my new application, but it'd be nice to still get power to that USB port for charging. Anyone know how that's wired up so I can get power to it?
  4. Amplifier wake-up signal wire: where does it connect to?? – The Suncoast wiring harness instructions are kind of vague on this, and there's like half a dozen different things I've read about how to wire up the amplifier wake-up signal wire to the point where I'm utterly confused. Some say to connect it to the antenna power line on pin 4 or 5 of the Quad Lock? Which pin exactly are people speaking of?
  5. FAKRA connectors: what are they connecting to? – I've read a handful of threads that talk about the FAKRAs, but mostly gloss over what each and every one of these is / is connected to. Any insight (or, even better, a diagram!) on these—if just for my own self-edification—would be much appreciated 👍🏼
  6. Should I hook this up to the amp instead?– I realize hooking all this up directly at the amp would probably be more straightforward wiring-wise, but I'm trying to make this as easily reversible as possible in the (however unlikely) event I ever want to swap the PCM back in. All the same, if anyone has any reasons why wiring things up to the amp would be more advantageous, I'm all ears.
  7. Am I missing anything? – As evidenced by the above, there's a ton I don't know about how all of this works (or really car audio, for that matter—I've never worked on automotive sound systems, so this has been a learning experience)—everything I've gleaned has been from the Suncoast radio harness wiring diagram, and a patchwork of searching the forums for folks that have done aftermarket radio swaps. That said, are there any blind spots I ought to be aware of? I just want to make sure I'm doing all my homework before removing everything.


Thanks for any info or feedback any of you can provide!

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