# Used car with a mp3 player jack mystery **URL:** \ **Category:** Factual Questions\ **Created:** [April 11, 2016, 11:52pm UTC](https://boards.straightdope.com/t/used-car-with-a-mp3-player-jack-mystery/751948 "2016-04-11T23:52:30Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [April 12, 2016, 8:04pm UTC](https://boards.straightdope.com/t/used-car-with-a-mp3-player-jack-mystery/751948/21 "2016-04-12T20:04:45Z")
> [@Really\_Not\_All\_That\_Bright](#): > > It might be a 3.5 mm plug after all. They come in surprisingly variable sizes; the OEM jack in the dashboard of my last Hyundai would accept any 3.5 mm plug but none of them fit quite right and I would only get mono audio output unless the plug was seated “just so.” Are you sure it wasn’t expecting a three-stripe/4-conductor plug, the ones where the last one is used for a microphone or inline controls? [Phone connector (audio) - Wikipedia](https://en.wikipedia.org/wiki/Phone_connector_(audio)#/media/File:3.5mm.jpg) ---
**Author:** ![SmellMyWort](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@SmellMyWort](https://boards.straightdope.com/u/SmellMyWort)\ **Post date:** [April 12, 2016, 8:26pm UTC](https://boards.straightdope.com/t/used-car-with-a-mp3-player-jack-mystery/751948/22 "2016-04-12T20:26:31Z")
> [@SpyOne](#): > > My LG cell phone has a socket for an earpiece with speaker and mic that takes a plug significantly smaller than the one used by iphones. > > I have seen devices that took power through a plug that looked a lot like a earphone plug, but smaller. > > There are any number of things that plug might be. Before I plugged it into anything valuable, I’d want to crawl under the dashboard and see where the wires go at least. Yeah, I’m guessing some sort of hands-free set up for the previous owner’s cell phone. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [April 13, 2016, 10:41am UTC](https://boards.straightdope.com/t/used-car-with-a-mp3-player-jack-mystery/751948/23 "2016-04-13T10:41:03Z")
OP could try putting a signal onto the pins… see the wiki entry for TRS … Tip ring shield… connectors for contact assignments. If it is for audio input, AUX , the stereo system has a way to select it ? If you can’t select it what use is it ? ( It could be for a microphone for handsfree alternatively.) And if it is for aux input, perpahs the tip can be reduced in size… or just replace it with a standard 3.5mm TRS ---
**Author:** ![carnivorousplant](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/carnivorousplant/32/3563_2.png) [@carnivorousplant](https://boards.straightdope.com/u/carnivorousplant)\ **Post date:** [April 13, 2016, 12:47pm UTC](https://boards.straightdope.com/t/used-car-with-a-mp3-player-jack-mystery/751948/24 "2016-04-13T12:47:17Z")
Check it with a voltmeter. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [April 13, 2016, 1:22pm UTC](https://boards.straightdope.com/t/used-car-with-a-mp3-player-jack-mystery/751948/25 "2016-04-13T13:22:10Z")
> [@Reply](#): > > Are you sure it wasn’t expecting a three-stripe/4-conductor plug, the ones where the last one is used for a microphone or inline controls? [Phone connector (audio) - Wikipedia](https://en.wikipedia.org/wiki/Phone_connector_(audio)#/media/File:3.5mm.jpg) Oh, maybe. I didn’t know that was a thing. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 13, 2016, 1:56pm UTC](https://boards.straightdope.com/t/used-car-with-a-mp3-player-jack-mystery/751948/26 "2016-04-13T13:56:32Z")
So this car stereo has a short cable hanging off of it, with something that looks like a 3.5mm stereo plug? And are you saying it’s too small to be a 3.5mm plug (i.e. it sits loose in a 3.5mm jack), but too large to fit into a 2.5mm jack? Does it have the same design as a 3.5mm plug, i.e. looks like a metal rod with 2 plastic insulator rings along its length? [Previous page](https://boards.straightdope.com/t/used-car-with-a-mp3-player-jack-mystery/751948.md?page=1)