So I'm going on my 2nd replacement PCM 3.1 and—quite frankly—having seen a slew of other recent threads detailing the same issues I've been having (namely the continual rebooting), I'm kind of at the end of my rope with dealing with these head units. Porsche clearly knows there's a systemic issue with them going wrong, but we're never really going to get a true fix; I'm really just picturing an endless string of trips to the dealership.

With that in mind, my original thought was to just go aftermarket (there's a ton of options, after all), but while I've been waiting for the dealer to get the (latest) replacement PCM in stock I've been getting by with just my phone and a Bluetooth speaker that fits in the cup holder and it's been…actually very liveable. To be honest, even with a working PCM I'm usually driving everything—radio, nav, etc.—off my phone anyway, with the head unit simply being a conduit to the car's speakers at the end of the day. And after watching one of the first-look videos of the GMA T50 where Gordon Murray talks about the car having a wireless-only setup paired to your phone (he starts talking about it at the 37:07 mark)…


…(and be sure to watch the rest of the video as well for some great engineering nerdery—this car is gonna be a monster), it got me thinking: why not simply remove the head unit entirely, install a Bluetooth receiver, and throw in the radio delete shelf for the 991/981?

With that in mind I found these guys based out of Indiana, as well as amps with Bluetooth connectivity. Anyone have any experience with either of these, or any other solutions? And to those that have done radio work, is there anything I ought to be aware of? I know I'll need the radio harness adapter that Suncoast sells, but anything beyond that? As far as I know, the system in my car is a standard, non-Bose setup, so it should have an amp under the passenger seat (gonna stick my head down there sometime tonight to check)—what, if any, issues might that present? I've also been searching for a wiring/pin-out diagram, but no dice, so if anyone has a copy I'd be super appreciative. I'm a car audio noob, so feel free to talk to me like I'm five years old.

Thanks for any advice & input you all might be able to provide!

 

I just use this and works perfect;

 

Thanks, but you still need a radio head unit for this to work, correct? What I'm proposing is deleting the head unit entirely, installing a bluetooth receiver connected directly to the speakers, and pairing my phone with that receiver, i.e. making the phone the de facto "head unit" (sorry if that was unclear).

 

I've thought about this too. I would try to see if you can go direct to the amp with a generic bt adapter like this one:
​​​​

 

I think that this is the one that I have


plugs into the aux jack and USB in the glovebox. Invisible. Nothing to turn on or do. Automatically connects. Flip your radio to Aux and it’s already connected.

 

I like this idea, however the amp still requires a wake up signal from the wiring harness, meaning I’d still have to mess around with the QuadLock bits. Plus I’m not sure of how much fettling I’d have to do in order to connect an adapter like this to the amp itself—presumably it’s not exactly a plug-and-play type of solution?

Still requires a head unit as far as I know; as I understand it, the USB and AUX are wired to—and require—the PCM to work. I could be wrong there, so any info to the contrary is more than welcome!

 

Has anyone figured this out? I have all the components using an Out of Sight Audio unit, but the wake up signal to the amp is stumping me. I measured 12v coming out of the PCM for that particular pin, but I get a ton of noise when running 12v to the amp wake up line even before plugging in the unit. I'm wondering if I'm missing something or need to run some sort of filter on the line.

 

So this project finally got tackled this week!

In terms of major materials, you'll need:

• Out of Sight Mark 4 Bluetooth receiver
• Suncoast Radio Harness Adapter (the system in my GT4 is the Sound Package Plus, so no MOST to fuss with—if you've got Bose, it's going to be a different ball of wax)
• Porsche Radio Removal Shelf

Some other odds and ends that I found useful:

• Tesa wiring harness tape really helps in tidying a project like this up so that it doesn't look like a rat's nest
• I got a ferrule crimper for the power and ground leads and it similarly helps to keep things tidy and provides a very secure connection
• Having a pack of T-tap connectors on hand is really helpful
• Terminal extractor keys are super handy if you need to pop out any terminals in the Quad Lock plug (e.g. I didn't need one of the wires in the harness adapter, so I took it out instead of leaving it dangling)
• Wire strippers!! Oh my god, why didn't I get a set of these sooner?! For years I've been using wire stripping pliers, but with stranded wire you always end up cutting a strand or two out. Proper wire strippers make things so much easier.

@lawlence (from the post above) got in touch with me late last year and related the couple problems he was having, namely that the minimum volume level was too loud and that there was a ton of crackling/popping. I’ll address how I solved those later in the post, but first I wanted to answer some questions that past-me had which might come in handy for others looking to dig into the radio bits of their cars:

1. What circuit(s) is the 12V radio power connected to? – the PCM is on a constant / always-hot fuse. The PCM itself controls the amp wake-up signal, so I wired the amp wake-up separately to a free switched fuse slot in the left-side fuse panel using an add-a-circuit tap. If you leave amp wake-up hooked to a constant fuse (e.g. if you tap off the PCM power wire), the speakers all draw about 5V, which is probably enough to kill a battery (I didn't check amps, but I think it'd be enough where were you leave it over a long weekend, you'd probably come back to a dead battery).
   
2. What wire(s) is the integrated hands-free microphone hooked up to? – Never figured out any mic stuff, but for anyone interested the mic wiring is in the blue plug on the Quad Lock connector (lower left):
   
   (This pinout is courtesy of an excellent thread on retrofitting a PCM4 in a PCM3.1 car)
   
   You can see there’s two mics indicated (which is evident on the top of the steering column), as well as a shield (which presumably gets connected to ground? I’m an automotive electrical neophyte, so forgive my ignorance). My plan at some point is to take apart the mic wire that came with the Out of Sight and wire up the positive connections & gang up all the negatives + shield on the 2.5mm plug to see if that is able to work; here's an article I've found informative on the subject.
   
3. Glovebox USB / AUX input—how are these powered? – Also didn’t work on any USB stuff this time around, but in the pinout above you can see some pins on the green plug on the Quad Lock labelled as “IPOD CHG” which I would presume would be for USB power. However in the service manual wiring diagrams (see PDF here) there’s a wire that’s labelled “VUSB”, which I presume to mean “voltage USB”? That bit honestly has me confused, so just as well I didn’t decide to tackle the USB port this time around. Anyone with knowledge on the USB wiring, I'm all ears.
   
4. Amplifier wake-up signal wire: where does it connect to?? – Pin 4 on the blue plug! (Labeled "AMP On" in the pinout) As I said above, probably best to wire it to a switched fuse in order to avoid power drain.
   
5. Should I hook this up to the amp instead? – When I was running into issues with buzzing/popping I considered this, but as you’ll see below there’s a solve. Short answer: yes, you could wire to the amp, but you’ll be taking out a seat, then splicing into the wiring harness itself or wiring up a plug to go into the amp. On balance, it’s probably easier (and less destructive) to just do all the work in the head unit area.

So what about these issues with loud minimum volume and crackling/popping when the amp was switched on?

The former issue is because outputs on the left side of the Out of Sight (i.e. the ones on the green block) are at speaker level; given that every Porsche sound system that’s Sound Package Plus and above has an amp (found under the passenger seat), the system is wanting line level output. This is further confirmed from this user who “[changed] the outputs [coming out of] the head unit from the speaker outputs to the preamp outputs” (side note: that thread has a lot of good info if you're looking to do a general aftermarket radio swap). If you have a CDR-31 I believe you'll want to use the speaker level outputs.

To solve, I used the pre-amp RCA outputs on the right side of the OOS unit, which output at 4V vs. 12V. For this I got some RCA plugs, ganged up all the positives and negatives of each side, and soldered them to the respective RCA lead. This results in a quieter max volume, but it's sufficient for my needs. If in the future I want something louder, I think I could hook everything up to the speaker level outputs and put a potentiometer between the OOS and the wiring harness to act as a volume ****. It's something I've briefly looked into, but I wanted to just figure out the basics the first time out.

For the buzzing/popping on amp wake-up: all the stock amps under the passenger seat directly contact metal, which creates a ground loop condition. I hooked up a ground loop isolator between the Out of Sight and the speaker harness adapter and it killed the buzzing right away. There's still a little buzzing, but it's a kind of high frequency noise always been present in the sound system even when the PCM was installed. The ground loop isolator also has some additional ground wires that I didn't splice into the ground on the harness this time around, but maybe I'll give it a try next time I'm in there to see if it helps.

And that's essentially it! Here's a photo of the entire setup before it went in:



It takes a little cajoling, but it all fits really snugly behind the dash. See here for a quick video of the unit in use:


You can see that the amp is powered off when the ignition is turned to "off", and powers back on in "accessory".

Anyway, that's it for now—if I ever decide to tackle the built-in microphone, I'll be sure to post an update. If you decide to take on this swap, please post your results!

 

OP, your solution is elegant.
Thanks for the details.

My car is radio delete.
I bought one of these for $35 on ebay.
certainly not "hi-fi" but adequate.
https://www.jabra.com/in-car/jabra-f...00-46000000-02

I can take phone calls and listen to pandora / podcasts = good enough for me.

 

Thanks for the compliment! I didn't know little loudspeakers like that existed, so that's definitely a good solution. In fact, when my PCM broke the first time around I ended up just using a little Bluetooth speaker for music—that one I linked fits perfectly in the cupholder, so it worked great as a short term sound-only solve.

I'm assuming your car is radio delete from the factory—does it still come wired up with speakers? @sonorous and I were chatting over the weekend about this project and we were wondering if factory radio delete cars came stripped of all audio components, or if they were wired up with the basics should an owner decide later on to throw in a head unit.

 

Just a quick update following some further poking around:

Glovebox USB/AUX connection – Mixed bag here. The AUX line is the entire green socket on the Quad Lock (part no. 99164212301)—given that you have access to the individual pins, you might be able to hack something together here, so coin toss for those willing to take a gamble.

The USB port, however, is connected via what Porsche dubs the "Multimedia interface", part no. 99164212201:



There's no messing with that without having to hack up the cable. So supplying USB with power is moot.

Handsfree Mic – So on this front I’m a bit more hopeful. The stock setup has 2 mics that provide a degree of noise cancellation, so I think trying to wire both up to the same output likely wouldn’t yield great results. Given that I have the pinout, I got a converter cable for the 12-pin connectors on the Quad Lock and I’ll try wiring up just one of the mics to a 3.5mm mono jack to see if that does anything. If that doesn’t work, however, @DriverDaily did some legwork combing through the PET and found that Porsche makes a mic that connects to a standard 3.5mm mono jack for the Japanese market; the parts cost are pretty reasonable, so I've ordered those just in case. If my hack-y solution works, it means I don't have to crack open the steering column cowling, but it's nice to have an OEM solution in the back pocket.

 

Some more updates on this project.

Glovebox USB connection – another member clued me in that the yellow end of the "multimedia interface" cable is a female HSD connector. I'm seeing if there's a way to source a male connector that I can then supply with 5V power for USB. Looks like this might be back on the table.

Handsfree Mic – unfortunately my plan of wiring up one of the mics to a 3.5mm jack didn't pan out. It was definitely receiving an audio signal, but it was extremely weak—my guess is that the PCM normally supplies more power to the mics than that of a standard audio jack. I've got the parts for the 3.5mm retrofit on order, so I'll post an update when those get in.

Alternator Whine – I was having an issue where there was a decent alternator whine as you worked your way up the revs. I checked all the grounds and everything was tight, but after doing some further reading I was lead to believe that an in-line noise suppressor could possibly help. Connecting the suppressor to the constant 12V wire that the Out of Sight is hooked up to yielded no results, but hooking it up to the amp wake-up wire did the trick. This and the ground loop isolator essentially kill all noise in the system.