Stereo Wired Remote

[TheMrBlue]

A few days ago I discovered that the remote wire input on car stereos looks just like a 3,5mm connection; so yesterday I decided to pull my stereo out & see if headphones with volume buttons would actually control it (I know it sounds ridiculous, but ya never know!).. Unfortunately the only thing those buttons do is shut down the stereo after holding them down a few seconds.

So now I was wondering if there are aftermarket remotes that plug into the stereo (or maybe something that could be easily made?). I want this because I did a very simple tablet install, and would like to more easily control the volume (and if possible input-mode) of my stereo.

Thanks in advance!