This came about from recent discussions, and some investigation:

To control the Alpine DIN 1/2 stereos or 2005 model radios that have a 1/8" jack on the back by hard wiring it to the remote (or other button-pad you made with guts of a remote).

Remove the Infrared LED from the remote to replace it with a 1/8" stereo plug.

Make a note of the LED orientation:
Click to view attachment

The larger side is the Negative connection
The smaller side is the Positive connection

Mark the LED+ and LED– on the board, then cut the IR LED off the remote circuit board.

Get a 3.5mm Stereo plug, and some thin coax cable from Jaycar, DSE, wherever.
Click to view attachment
Click to view attachment

Connect the centre wire of the coax from the tip connection of the 1/8" plug to the LED+ on the remote board.

Connect the outer shield wire from the outer ground shield connection of the 1/8" plug to the LED– on the remote board.

The middle (in-between) conductor of the plug is not used.

YAY!!!

Another alternative is the KRE-500A. It is a remote eye (or infra-red receiver) that plugs into this socket, made by Alpine. It costs $39.00 RRP Inc GST. I know it works on DVD based head units, (where you can select "Remote Rear" in the menu). I'll try to find out if it works on the rest of the decks with the jack on the back. (CDA-9851 - upwards)

Its just another alternative if you're not too confident ripping your remote apart. It will also give you the ability to mount the remote, with the eye in front of it (as I have done in my centre console), and still have the ability to pick up the remote and use it like normal - best of both worlds!

Or Pulse-R's instructions will give you the ability to flush mount the remote into a panel for a really schmick custom job.

If that's the case, why use a stereo plug rather than mono?

Something to do with a mono plug shorting out the middle to the ground - the deck has a stereo socket, maybe to power an external circuit of some description (such as a IR LED receiver - I hear they are $39.00 or so)

perhaps this is a way to power the remote so you don't need extra batteries???? - maybe I'll look into this and include it in the tute...

I have been told by a reliable source, that the middle conductor is a supply for the eye, so could be used to power the remote... perhaps someone at Alpine can look at the circuit to see what the maximum current would be for this?!?!?!?!?