"If it ain't broke, don't fix it"

My car, a 2016 Honda Accord, works just fine. That being said, although it's not broken per se, it could be better in some ways. So, in accordance with my true spirit – fixing problems which aren't real problems – I decided to fix this one minor inconvenience with regard to my car.

When it comes to the head unit (the audio/entertainment/navigation screen & unit, which I'll just refer to as "radio" from now on), two things have always slightly inconvenienced me:

1. Sometimes, at really long stoplights, I'll turn off my car.
   I know there are many people who disagree with this, as it wastes the life of the starter. I mostly do this for my own peace of mind, just because it makes me feel better; even though it may make very little difference, I feel bad knowing that my engine could/should be off, and that I'll have ample time to turn it back on before proceeding.
   
   Anyway, back to the point: when I turn the car back on, the radio shuts off, and I have to wait about 20-30 seconds for CarPlay to reconnect. This is because the 2016 Accord was a relatively early adopter of CarPlay, so things weren't fully ironed out yet. In my mom's 2018 Honda CR V, CarPlay connects and plays music in <5 seconds!


2. Whenever I get to my destination and turn off my car, the radio (understandably) turns off.
   However, in my dad's 2019 Acura RDX, it stays on until a door is opened. It's just one of those cases where you catch a glimpse of what could be, and then you end up wanting it for yourself. A.k.a. jealousy.

There are also some things you should know about me:

1. I love cars.
   They're amazing little machines that go incredibly fast, are full of more bells and whistles than imaginable, and are even capable of semi-autonomous driving. They're amazing!


2. I have absolutely no clue how they work.
   Not in the slightest. Actually, I have no clue how quite a lot of things work.

That second point in particular is what has motivated a lot of my projects. Just like everyone else, I'm interested in learning how things work, and there's no better way to learn than firsthand, by doing.

My projects, like this one, are just a way for me to dive headfirst into an unfamiliar area of interest. In this case, the areas of interest were extremely low-level electrical engineering as well as basic interior car work and component wiring.

It all started when I (14EXLV6) made the following post on the Drive Accord forums:

Hello all,

I have a 2016 Accord Touring (as well as a '14 EX-L V6, lol), but I'm interested in whether it would be possible to make the head unit remain on until the driver door is opened. Currently, even if the engine is turned off, as soon as it is restarted, the head unit also restarts. Why? Is there any easy way to rewire things?

Sorry, I'm very much a noob when it comes to car mods. If I were to do this, I'd definitely have a shop near me do it. But I just wanted to know whether it would be feasible. Has anyone done it before?

Thank you for your input!

-14EXLV6 - 14EXLV6 (me)

Multiple forum members were nice enough to reply to me and chime in with their thoughts:

Yes, but you will need to retain power to all downstream devices as well. - sandevino

Technically, this probably could be done but it would take a good amount of custom work. I'm no technical expert, but I think you could hook up a relay to the power windows and use that to trigger when the power is fed to the stereo. But I'm not sure how well that would work since the stereo is interconnected with a bunch of other things in the car. It's an interesting thought but I wouldn't bother. - flamup

Then, things pretty much went dead for eight months. As a college freshman, I started to become busier as the year kicked into gear and forgot about the minor inconvenience of my radio turning off.

Quarantine (COVID-19)

That all changed when the world was upended, when I was locked at home with nothing to do for the forseeable future. I always wanted to develop some level of proficiency in basic electrical engineering as well as see how some of the electronics work in my car; this project was a great introduction to both of those areas, so I decided to start with a plan.

I began by looking at the wiring diagrams for my car's radio:

It showed that the pin I was interested in was on Connector A, the main connector (car radios nowadays have quite a few connectors - for power, for the speakers, for the backup camera, for steering wheel controls, etc.). The pin number was Pin 24, which I could easily see in the diagram Honda provided. Connector A + Pin 24 = A24, for short.

Something interesting to note is that the radio is always connected to the battery via pins A3 and A1, which are power and ground, respectively. Pin A24, labeled "ACC" for "Accessory," is connected to the accessory circuit and acts like a switch. Whenever the accessory circuit has power, the radio is supposed to turn on, as do other components like the cigarette-lighter 12V power outlets.

I called up Crutchfield Audio, one of the best stores in North America for aftermarket audio system work, and asked if they thought my plan might work - to "hijack" pin A24 and connect it to my own circuit. They said that they "didn't see why not," so I began to plan.

With the help of my great friend Dominic Assia (many, many thanks!), after exploring our options for a few hours, we drew up the following schematic:

The most notable things are:

• It's super, super basic/informal, and I apologize to anyone with a proper electrical engineering background who might be cringing at the errors, e.g. using the symbol for Earth ground rather than chassis ground, etc.
• I included a lot of inline connectors (»), so that if I messed up one part of the project, the mistake or damage would be relatively contained; I could just unplug it from the rest of the system.
• Though the schematic included flyback diodes for the relays, I ended up not using them because 1) I was afraid of damaging the diode by heating it too much when soldering it, creating a perfect part for a short circuit; and 2) They didn't seem terribly necessary, as the relay boards I used had some (low-power) diodes already. The flybacks were more of a nice-to-have, I think.

Once the schematic was finalized, I began to order parts from Amazon. Most of the costs at this point were simply for my soldering kit, which I had to compile from scratch.

Parts

Project-Specific

Item	Qty @ Cost	Notes	Link(s)
Programmable Off-Delay Relays	2 @ ≈ $16	You just need an off-delay relay with a "signal-hold" function. These relays had many modes + a full LCD, which was not preferable, but I got them because at least I knew they'd do what I needed. The exact relays I purchased are currently unavailable on Amazon, so I have an alternate link for relays that seem identical (and cost less!).	DROK (Amazon) Alternate (Amazon)
Low-Profile Mini fuse Taps (10-Pack)	1 @ $8.97	My car, a 2016 (9.5 gen) Honda Accord, uses low-profile mini fuses. I believe (but am certain) that all 9/9.5 generation Accords use this style fuse.	Amazon
2-Pin 16AWG Automotive Connectors (5-Pack)	1 @ $7.99	Probably overkill for this interior application, but was a solid & cheap option	Amazon
Inline Pre-wired Rocker Switches (10-Pack)	1 @ $7.58	Not very necessary, as connectors (very near) could simply be disconnected, but a nice-to-have	Amazon
Wire		< 20 feet total. Around 16-22 AWG should work, and I got 18 AWG since I didn't have any wire at all.
26-22 AWG T-Taps & Connectors (25 pairs/pack)		Not really necessary - I just had them laying around for another project. Hardwiring is fine, but I wanted a connector between my harness's A24 wire and the wire that ran from my fusebox to the back of the radio. Also, any other type of connector (bullet, spade, etc.) should work fine.	eBay
DROK Relay Board		I also designed and 3D-printed the following part, designed to hold the 2 DROK relays which I had purchased as well as serve as a way to secure them to the car (via the rectangular loops for zipties):	STL File
Grand Total

Soldering Kit

Item	Qty @ Cost	Notes	Item Link(s)
Soldering Iron	1 @ ≈ $27	I bought the version with only 1 tip, which is currently unavailable on Amazon. So, I've linked the next least-expensive option, which is the same as mine but with 5 extra tips for about $5 more.	Amazon
Heat Shrink	1 @ $7.99	580 pcs. assorted pack	Amazon
Tin Lead Rosin Core Solder	1 @ $8.59	0.8 mm, 50g	Amazon
Wire	1 @ $7.58	18AWG, 5-pack of assorted wire colors (5 m/16.4 ft per spool)	Amazon
Grand Total

Although Attempt No. 1 wasn't successful, I learned so much from it. All in all, I had the pleasure of seeing more of the inside of my car than I had hoped and ultimately learned that I am exceedingly bad at calculating risks.

Before all of the parts arrived, I wanted to remove the head unit to get experience, to make sure that I could do it when it came time to install my harness. This turned out to be more of a challenge than I assumed, but solely due to my own ignorance. I followed this YouTube video:

Note the following screenshot from it:

After calculating the risks, I decided that it wasn't worth the time to place the cloth. Well, what do you know. The right screw fell into a no-fun zone, which then led to the inside of the front dash. It was gone.

So, while the adrenaline began pumping (my entire family told me not to do this project, as I don't know anything about cars [but that was the point of doing the project...]), I followed this YouTube video to slide back the center console panels and this YouTube video to open up the lower dash cover on the passenger side. Luckily, after a few minutes of searching, I was able to find the screw, close everything up, and think about how lucky I was for a few minutes.

A few days later, the parts arrived, and I set up my soldering station in the garage. Once I could decently solder two wires together, I created the following "harness" (more of an extension cable than a wiring harness):

The plan was to plug the male factory connection (technically female, but I'm going by the connector rather than pins) into the female end of my harness, then plug the harness's male end into the female port on the radio. Finall, I'd connect the red wire to my own circuit as diagrammed in the schematic. Well, that didn't go so well, because I bought parts thinking that my car's connector looked like this:

While it actually looked a whole lot more like this:

...which I discovered way too late. See, not putting down the cloth was not the only risk which I had incorrectly calculated that day. Since I was already fully exposing the head unit (but not fully unplugging & removing it), I could have rather easily have checked what type of connector I had.

Instead, I trusted online retailers' websites, including Metra, the manufacturer of the male/female harnesses which I soldered together, and Amazon. While this wasn't a particularly dumb thing to do, it would have taken less than a minute for me to have physically checked.

So, with a heavy heart, I wasn't sure what to do. Since every online retailer had recommended those parts for me, I wasn't sure how I'd find the actual connector. Luckily, car manufacturers often share many, many parts between their cars. For example, something like a window switch doesn't need to be reinvented for every model. The same sometimes theoretically goes for electrical connectors, but with a huge catch:

Because very many possible feature combinations exist for cars, there is no guarantee that the connectors in your car will be fully pinned compared to other cars, or that they will even be the same. Manufacturers are always adding features to our cars, and every feature is just another wire or connector that needs to be plugged in. So, this was far from a guarantee.

Regardless, I was lucky in this case for two reasons:

1. This was Connector A, which supplied power (among other things), and was thus more likely to be found.
   Some rarer connectors, e.g. one that connects the car's parking sensors would be harder to find. Since aftermarket manufacturers want to make products with the highest demand, the more niche a feature/connector, the harder it will be to find fitting parts for it. Every Honda with a radio, regardless of its additional features, needs power. Thus, my hope was that I could possibly find another Honda model with a similar release year which used the same "A" connector.


2. My project was extremely simple.
   I didn't need the wires to be spliced in a particular way; I just needed a male and a female connector. Once both connectors were fully pinned, I just needed each of the 24 connections to connect to the one on the other side. It didn't matter what it was connected to, as I could simply cut, strip, and solder. Ultimately, all I really needed was 2 connectors and some wire.

I was the tiniest bit familiar with the 2016 Honda Civic refresh, whose new radio's interface looked suspiciously similar to my Accord's: I wondered if they might share their radios' A Connectors. Well, I went on Metra's website to discover the AX-DSP-HON2, a wiring harness whose connectors looked like this:

I was pretty much sold. All I needed was those two left connectors, which looked very similar (but not identical) to my cars', and I could cut off the others and solder their wires as appropriate. Also, all 24 slots were pinned, meaning that I only had to purchase one unit.

Last time, with Attempt No. 1, I had to buy multiple female connectors, pull the pins out of one, and re-insert them into the other. That process was especially difficult for me, a novice, so I wanted to avoid it the second time around if possible.

I ordered an AX-DSP-HON2 from ABT Electronics, prayed, and tested it out when it arrived. It fit! It plugged into the car's male factory connection and into my radio, though those other three connectors were just dangling. I got to work and, after a few hours, was left with this extension harness:

Some of the wires in the harness directly connected from the female to the male Connector A, which made my life easy. However, 8 of them went from the female Connector A to Metra's own connector, and 8 of them went from another one of Metra's own connectors to the male Connector A. So, I cut those 8-pin connectors off, and soldered each wire to its counterpart.

---

Looking back at a picture of the AX-DSP-HON2:

It appears that I may not have chosen the best way to do this. It seems that the 8-pin connectors may plug directly into each other (whereas normally one is the input to Metra's DSP-X device and the other is the output). I would need someone to verify, but if the corresponding wires match up perfectly, then you can simply connect the 8-pin connectors together... In my haste, I didn't think – I just did, sticking to my plan the whole time.

---

Rather than soldering the A24 wire directly to my circuit, I used a 26-22 AWG T-Tap so that if I needed to change anything, it would hopefully be less of a hassle. So, with everything plugged in, the back of my radio looked like this:

(Ignore the green wire with the pink connector on the right side of the picture, as that T-Tap is for another project which I did.)

Once everything was wired up and put back together, the final layout of all of the components looked like this:

Finally, below is a demonstation of the final setup of the DROK time delay relays which I used for this project.

And, again, the final product:

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Thank you very, very much to the following people for their help and support on this project:

• My family
  
  It's not that this project was particuarly difficult; it's that I have historically proven to be what you might call "mechanically-challenged." So, I can't thank my family enough for giving me the opportunity to go through with this project (especially being that it was my first). Thank you for taking a chance on me and for allowing me to tinker around with one of the most valuable assets that you own.


• Dominic Assia
  
  Dom, thank you so much for all of the hours that you helped me with this project, among others. I bothered you at night, at work, and pretty much every time I had a question, and you were always way too nice to me. Thank you not only for your advice, but also, more generally, for your friendship. I'll never be able to fully express how glad I am that senior year turned out the way that it did! :)


• DriveAccord.net Forum Members
  
  Thank you to every single person who took the time out of their day to chime in with their thoughts. I really appreciate it! Also, 17TouringCoupe, thank you very much for your kind words and support – it really meant a lot to me.


• Professor Sims
  
  Thank you very much for your feedback on my website and for all of your help. If it weren't for you, I don't think I'd have ever put in the time to complete this write-up (among others). Thanks to you, I will always have these project stories to look back on.