So this project finally got tackled this week!
Since I’d originally posted, another forum member had got in touch with me saying he was undertaking the same swap and was running into a couple problems, namely that the minimum volume level was too loud and that there was a ton of crackling/popping. I’ll address those further in the post, but first I wanted to answer the questions that past-me had:
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).
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):
PCM3.1 Pinout
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(The above 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.
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 attached PDF) 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.
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.
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.
I’d mentioned another forum member that had gotten in touch saying he was having issues with a 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 (vs. line 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”. 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 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 knob. 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 that 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 kind of it! Here's a photo of the entire setup before it went in:
out of sight audio
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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".
Some 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 (you can see one tapped into the yellow power lead that I initially used for the amp wake-up signal; it's unused now, but could come in handy later)
Terminal extractor keys are super handy if you need to pop out any terminals in the Quad Lock plug (I didn't need the antenna wire, 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.
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!
981 Porsche Cayman - Nav Wiring Diags.pdf