Trouble wiring in aftermarket double din stereo

Hi all - I have been having some struggles in trying to replace my CDR 24 stock audio unit with an aftermarket one (BOSS BV850ACP). I thought this would be extremely straight forward but I can't get my new unit to power on with the Key in ignition or with the car started. Im not sure what is causing the issue. From my set up, I believe Brown wire goes to car Ground, the white wire is power antenna, and if im correct the red/green is my Battery (Constant 12V) and the red/black would be the ignition. I connected them up to the new unit that way, but I cannot get any power. I've been trying to do some digging and posting online and some people are saying you need to use a fuse tap in order to successfully connect to a new unit. Has anyone successfully done this with a 2008 gen Cayman? I ended up buying the fuse taps, but Im not sure how to use them either so I will need to research. I was told I can tap into an empty slot, but how would I know if it is 12v from it, I was only able to find its Amp rating. I really have no idea how to fuse tap there does not seem to be an end to end write up from someone with the same car attempting the same install unfortunately. My last experience swapping out a radio was in a 92 Honda Civic like 20 years ago now. It was very smooth though so I am hoping I am capable of doing this without resorting to bringing it to a shop. Can anyone give me any tips? Its very weird, I used a multimeter with those wires and everything looks like it should be ok, maybe with exception the red black. But I would think the constant battery would be enough for the unit to light up for me after reconnecting the battery. The illumination wire is supposed to be optional, so I dont think its necessary to worry about right now and I have red that you need to tap into another wire for that but I will cross that bridge later. If anyone can offer any advice I would be extremely grateful, I have been stuck for a few days now retrying to connect it. I can't get any feedback from the site I bought it from but I dont think that the unit is bad.

I'm happy to help, but it sounds like you may be over your head on the task... or confused about using some of the tools? I'm not trying to offend you, but you say you know how to use a multimeter but then you can't tell how to know if you have 12V on an empty slot? I haven't done the install on these cars, but I have done it on MANY cars, so, again, I can help talk you through it, but I do need to know what you have for tools and if you know how to use them, etc, so I know how much detail to provide. To begin with, how did you use the meter to test the existing wires? What, exactly, did you do for tests? I assume you're using an install kit of some kind. Is it the correct kit for your car? There are differences between the various option levels ( Bose , etc)... do you know which one you have in the car, and whether the kit matches? I would start you off with just getting the power to work. For that, all you really need is to get power and ground working... maybe the always-on power as well. That's literally 3 wires. Once those are working, we can figure out the others.

hahah, well, I'm sorry to have made that impression. I am struggling to articulate the issue I'm having well, and I am still learning how to use some of the tools properly or with confidence. I've never been required to use a multimeter before and as mentioned my previous install was straight forward - wire to wire, turn it on and it worked successfully. From the multimeter, I was able to verify the 12v constant was wired fine, but I am not sure the switched power is working correctly. I mentioned that in hopes someone who's done this might be able to comment specifically since I have come across a few forum posts where there has been mention of needing to wire in a fuse tap or use the tail light or cigarette lighter as a substitute. Unfortunately these posts aren't detailed, and some of them are closed without instructions or if it worked. The kit purchased from my car I had gone back and forth with a great seller from eBay and we established my stereo which was the stock Porsche, non fibre optic, and I got a Connect2 fascia with a iso connector harness but the thing does not plug directly into the BOSS so I am wiring it in. I am trying to start with only that. The wire based on the pinout from the cdr24 ( https://www.pelicanparts.com/techarticles/Boxster_Tech/88-ELEC-Radio_Install/CDR_24_Pinout.pdf ) My Cayman has pins A2, A4, A5, A8. I identified the wires to connect to the Boss system as follows: Cayman Boss A2 (12V Switched) Red/Black 12 Volt Red Accessory A4 (12V Battery) Red/Green 12v Constant Yellow A5 (Antenna output) White Antenna Output Blue A8 (Ground) Brown Ground Black The BOSS unit also has some extra wires, like an Orange Illumination Wire, a blue/white Rem. Output (no explanation in the manual), an SWC Input wire (I am not sure what that one is for), and camera power - but I do not think these are necessary to hook up for the unit to power on - we should be able to see it turn on without those if we hook up the power and ground successfully unless Im wrong. Again the manual does not specify that but does say to tape up unused wires or connectors. The iso harness provided actually had 5 pins - but my Porsche's stock one had only 4 and 4 wires with different positions than what was in the purchased harness - so I pushed out the pins and replaced them into the correct slots so it would plug into the existing CDR connector - which is the one pictured in the original post. After soldering the wires from the boss connector to the iso plug, and then connecting that plug into the Porsche existing plug, I reconnected the battery and tried turning the ignition over even but the head unit did not power on. Thats when I tried testing the wires with my multimeter. Im not super familiar with the tool, but I looked up how to check the volts and could see for sure the 12v constant was working and I was using the ground to test as well. Actually what I am meaning to say with that sentence is that someone told me I can tap into an empty fuse slot on my panel - but they did not go into detail unfortunately and haven't followed up with my reply for some extra instruction. When it comes to fuse tapping, yes, Im way over my head I've never heard of it before so I need to look into it. From this page Porsche Cayman 987 (2006 - 2013) – Fuses Box Diagram and Amperages List - Stuttcars 2006-2013 Porsche Cayman Fuses Box Diagram and Amperages List This fuse box information is ONLY for the following Porsche models and years: – 2005 to 2013 Porsche 987c Cayman and Cayman S – years 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 and 2013 Fuse Box Location The fuse box in the... www.stuttcars.com . I was told I could leverage C2 as its empty Row C Fuse no. Description Amperage Fuse 1 Unused 7.5 A But I have no idea how to do that. First, it never says specifically that its 12v, only that its 7.5A. And also, if I am tapping a fuse the fuse tap has 2 fuse slots, so if im tapping an empty fuse, do I put one 7.5A fuse? The instruction confuses me because it wasn't also clear if this was suppose to take the place of the 12v constant or the 12v switched. Im a bit hesitant to plug things into the fuse box and wire in things though without someone giving me some confidence through instruction which is why im trying to confirm and get some clarity If you need a bit more info to help, please let me know I really appreciate your reply.

A few quick replies - I will see if I can read and process more comprehensively tomorrow. A few wire answers: Antenna Output - you may want to skip this for now... not needed, and may not be needed at all (I think these cars have an amplified antenna, in which case you might need it eventually, but for our power-up test, skip it. Illumination is used to proportionally control the radio "brightness" along with the rest of the dash. This is another one to skip for now - skipping it means it will remain in "daytime" mode for now, which is brighter. SWC is for steering wheel control signals - skip it for now. Blue/white remote output is to send a signal to amplifiers to tell them to turn on when the HU is on... again, skip this for now. Start with just the 2 or 3 power wires - switched, constant, and ground. I'll assume you have them setup correctly (I haven't checked your work yet). To use the meter - set it to voltage. Connect the black lead to a ground point. You can use the pin on the connector, or you can use most metal surfaces in the car - I sometimes use the latch for the door. Note not ALL metal surfaces are grounded... you might have to find a good one. Then, leave it connected there... that will be your reference for all measurements on the red lead. Move the red lead to the wire/contact you want to measure... if it's powered, you should see 12V reading. Note, we're calling it 12V, but on cars it can be anywhere from the high-11V up to 14.4V (when the car is running)... consider all of these as 12V for simplicity and that's good enough for what we're doing here. Generally speaking, all voltages in the car will be 12V. The 7.5A is a measure of current. Don't worry about that yet... just know that it will still show 12V. First,, check to make sure the ground pin is working. This is a little different - set the meter to "ohms" or resistance mode. This will measure resistance between the red and black leads. Leaving the black on the ground, touch the red to the ground pin on the connector. You should see a small amount of ohms here (less than 2 ohms total... I typically see 0 to 1 ohm). This proves that the ground wire is actually working. Once that's confirmed, turn the meter back to voltage mode, and check the power leads. Start to check if constant-on is working - it should be 12V all the time (regardless of ignition position). Then check the 12V switched - it should show 12V when the car is "on" (not necessarily running). If those 3 are working, then try reconnecting the stereo and see if it lights up - it should, ideally. Start there... and let's see what you get. If you have any questions, or if I've missed anything, let me know... I'm happy to explain further.

Ground + Constant looks good Ground + red/black (switched/a2 plug ) nope. Even when key is in the ignition and turned over once but not fully to start the car, I get 0.001v reading. So it’s definitely the switched 12v that I need to try and find/fuse tap into I guess. This is coming directly from the plug from the stock receiver so nothing is tapped yet, I was hoping that everything was already ready to go from the original unit but looks like this is where it gets tricky. In that pelican parts link, it says the cdr24 has a plug C which I do have but it is not set to be harnessed into anything from the boss. One of the C plug settings from the legend in the link says it controls the on/off with a signal if the key is inserted. I wonder if this needs to be bypassed it does say not to confuse it for 12v switched but as mentioned, my 12v switched doesn’t behave as expected. The original cdr24 powers up fine and works if I put it back in though, so it’s odd it would work for the cdr24 but not for an aftermarket unit?

Ok, good work! I wonder if the car tries to communicate with the CDR24 or something (over CANBUS, using constant power to operate) before it provides power to the unit over the switched output. Seems silly to go through all that, but this is a silly car sometimes. That said, this may be why people say you "have" to tap an unused fuse point... which is easy enough to do, so I'd recommend doing that. To do that, go over to the fuse panel and use the meter again. Set it to voltage, setup your ground lead, and then probe with the red lead. Basically, you're looking for slots that are empty and probe the contacts. Note, in a fuse panel, one contact will have power, the other will not... because what's happening is that the panel provides power on one lead, that goes through the fuse, and then out into the supply leg for the circuit it's delivering power to. Pretty simple. (Incidentally, this is where the "7.5A" (= 7.5 Amps of current) is coming from... that's the max current they designed for that circuit, that's all... hence you don't want to use a fuse larger than what it was made for...but you don't have to worry about that here, I don't expect... but we can check once you get further along.) So, do the meter thing, probe around the panel looking for open terminals with switched power. On my 2010, I found the cell phone terminal was useful... I used that as a tap for my radar detector. I forget how many Amps it was rated for, but an RD takes like 500mA (=0.5A) so I knew it wouldn't be a problem... Once you find a suitable terminal, for now, you can simply run a wire from that terminal to the radio, and see if all that works to power it up. If it works, that's going to be where you will want to tap in the future, so it's just a matter of planning out the wiring run to make it all happen cleanly. At that point, we can figure out what fuse you need and how to place it there. Take a peek in the HU (Head Unit, aka the radio in the dash) manual and see what it says. It should tell you somewhere what the current draw is. Are you having fun yet? I kinda enjoy this stuff... as you can see...

Haha - it doesn’t deter me when things get a bit tricky, but I’m hesitant to say I’m having fun just yet. Some things that Im not clear on is this - there seems to be two suggestions and it isn't clear what path to follow. 1) Look for an Empty Fuse Slot If I look for an empty fuse slot, then how do I know its going to behave similar to the switched power would? In this case would it not be a constant 12v? for example Porsche Cayman 987 (2006 - 2013) – Fuses Box Diagram and Amperages List 2006-2013 Porsche Cayman Fuses Box Diagram and Amperages List This fuse box information is ONLY for the following Porsche models and years: – 2005 to 2013 Porsche 987c Cayman and Cayman S – years 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 and 2013 Fuse Box Location The fuse box in the... www.stuttcars.com fuse%20box So this does not tell me its switched, I would assume its 12v constant if I tap into it. If I do this is that a problem? The stereo would then need to have a power off or it will drain the car no? If this is the path to take, I have more questions but lets first identify if I should use this or #2 2) Tap into an existing fuse. If I am understanding this correctly, I would then take say the above Row D, fuse 9 and branch from here to try? I wonder what would make for the same as switched power? There is a spot in Row C that says Key Module, would that turn on as the key is in the ignition? Or what would make more sense? When I come across peoples posts saying they did it by running to the tail light, are they meaning that they used a fuse tap to get into one of the slots? That sort of makes sense I guess because those lights are only on if the car is on? but you can also turn the lights to on with the key out. Could it be that All of Row C is related to the Key being in? Since I can see it is stuff like "Diagnostic Socket TRM15, Klimatronic Control Unit TRM15, PASM Control Unit TRM15, Refrigerant Pressure Sensor TRM15, Clutch Switch, Electronics Box, Mobile Phone TRM15, Heated Spray Jets" This spot I would think needs the key to be inserted to have power. Do any of these questions make sense?

Not all in a row will necessarily behave the exact same way, so don't go by that. The method to find switched power is to use the meter. Setup ground, use the red lead, and look for contacts that change voltage with the ignition. If you can find a blank one, then that's easiest. However, if you need to tap into an existing fuse, you can do that as well, but I would use a purchased product for that. Something like this: https://smile.amazon.com/JABINCO-Circuit-Adapter-Blade-Holder/dp/B0827L4HH9 As you can see in the second picture, this plugs into the existing fuse, and gives you two ports for fuses to work with - one is to fuse the existing vehicle circuit, and the second is to fuse your new "tapped" one. Again, you only really need this type of device if you are tapping an existing fuse. I recommend trying to find an unused one if you can, first, as this is cheaper... but either of these methods can work, as you can see. Note, I didn't check the above-linked part for compatibility with our cars. I merely used it as an illustration - if you decide to do this, be sure you buy one for the correct fuse time in the car... it may be this one, but I don't remember off the top of my head. (The kit I bought had taps for each type of fuse... and I don't remember which one I ended up using on my car.)

I’m a bit ahead in that I’ve already purchased the tap. It’s here with me. Am I wrong in thinking that I can just plug the tap into the empty slot? If I do this - if it’s the empty spot I only need one fuse then? And if it’s an existing one I need two of the same fuse that it’s being tapped into? I will try the empty spot with the tap and just use the wire end to test positive for if it’s got 12v. thanks for the help!

Yes, if you use an empty slot, you only need the a fuse for the "tap" leg. (Actually, if you look closely, you may see that there is no "other end" contact for the empty fuse socket anyway, in which case having a fuse for both won't hurt anyway, as the power won't go anywhere... I believe that's what I have on my cellphone unused tap.) And, yes, if you are tapping an existing fuse, then you'll need one there to keep running whatever you tapped off. Yes, good to check the tap end to ensure you're getting 12V there!

Great news! I got the 12v from that empty slot, it kicks in once the key is turned so it will be perfect for switched power. I think my only issue now is I need to know what the connector plug to buy would be - I guess I could strip and solder the wire in directly tho too. Just trying to make something look more clean though. Can you recommend that type of connector and the wire gauge? I believe it’s 16awg or something, as that’s what is labeled on the tap wire, so I bought that but I’m skeptics of the 22-16awg male connector pin that they sell, it’s 0.157 diameter I think and looks too big to slot into the plug . I suppose I could snip the end and wire it in but I would prefer something cleaner looking if you are able to help recommend the connector

Awesome! Again., kudos for your continued pursuit on this, and posting back here with great details. This might be a good thread for any beginner to look at and learn from, so thanks for hanging in there with me on this! I think you're next question is how to tap that power into the wire properly. Many ways to do this... how have you done it so far (photo might help so I get an idea of where you are with the process. I typically do it one of two ways - one is to solder and heatshrink. This is good for wires of differing sizes. However, generally you want to match the size if you can, so you match the current-levels needed. You can certainly solder/heatshrink matching sizes too, of course. If you have crimpers (even the cheapie ones like this https://smile.amazon.com/Klein-Tools-1001-Multi-Purpose-Electricians/dp/B000EVLUR2 ) than an insulated blade or barrel connector is a good alternative - no soldering needed. For example: Or And there are also butt-connectors that could work, but these don't disconnect, so I prefer not to use them: Any of these work reasonably well with the cheap crimpers I mentioned. Just make sure the connection is secure (pull it after crimping, to make sure it doesn't pull out). If the wire you're using is a little too thin for the connector, I sometimes fold it over to make it "thicker" in the crimp barrel, before crimping. The fancier/official way of doing this would be to use ferrules, but you can get away with the fold-over method in a pinch (and save yourself from having to buy more tools if you don't want to). So, basically, cut the wire on your radio harness (NOT the car!) and join it as needed with your newly tapped wire. And that should get you all set there. Once that's done, connect the other wires as needed... let me know if you have questions on those. I would connect the illumination and any others that might seem important. And, of course, all the speaker wires. I would suggest trying everything before pushing the radio in all the way, if you can, because you can troubleshoot faster that way. One other thing - before the final push in, be sure you test with the engine running as well - the reason is that sometimes electrical noise from the running engine makes its way into aftermarket radios (more than factory ones)... so if that happens, you will want to troubleshoot and fix that before pushing in. This can get a little tricky, but I'm here to help if you run into that... Also, try to keep the wires as short as possible behind the radio, because there is rarely enough space back there for all of them to go... so less wire is easier to pack in. Just be aware, that last pushin can take a little effort and time to get done right and clean enough. Sometimes if you jam it all in there you'll break a wire or something, so be careful with that, too!

Thanks will definitely be updating with more photos and hopefully complete success soon - I am probably going to solder it and do away with connectors for now. Any advisements on how to hide the wire? I think I have to remove the interior covers in the feet area, is this going to damage stuff taking it apart or is it fairly simple for ppl?

There are literally dozens of "how to" threads for installing an after-market head unit in the 987. I know because replacing that horrible CDR30 was the first thing I did in 2010 when I bought my new Cayman. I hope they didn't disappear when the site got re-hosted a few years ago. There were actually illustrations on how to tap-in to get the needed switched +12VDC including which existing fuses to use. Most installers used B6 or C9. Retaining "key sense" with aftermarket head...

I came across some others but cdr30 is with an amp and fibre no? I have a different model, cdr24 is different and I mean no harm with something else being out there. I suppose I would have had to know what to search better for if the terms retaining key sense was a good term I was not familiar with.

The specific issue I was addressing was adding a "switched" circuit. This is the same regardless of CDR24 or CDR30. And yes that thread title isn't something you would think to search for. I only used it as an example since it was one I was familiar with (actually I found it mentioned in a different thread. BTW, it is better to use google or some other search engine than the horrible search engine built-in to Planet 9.

Thanks for the help! Everything turns on as expected now, I only need to finalize the routing and put everything in for good.

Here’s the finished install look if anyone was interested

Ooh, that looks pretty! I'm in the process of picking a new HU for my 2009, so nice to see this post and the final result. Update: Jan 8, 2025 (very delayed, as this has been in for a couple of years already). Bought a Pioneer unit and a SiriusXM antenna. Have travelled across the country with it and it's nice to not have to change channels all the time with either Sirius or Spotify .

Hey I have the same problem, so the black/red is dimmer? And red/green const power? Brown is ground but I have a yellow what is that for? Ty

Hey did you connect that to the car harness? To the black red wire? Or direct to the head unit red wire?