How To: Connect your factory AUX jack to RCA's on an aftermarket HU.

[tranceFusion]

So I wanted to get an aftermarket head unit but I really liked having the AUX jack. I have an Si Sedan. I haven't seen all the information to do this in one place so I thought I would make a new post using the info I got from various threads on here and some other sites.

What you need:
- RCA cable with red and white connectors
- Wire cutters/strippers

What you SHOULD have to make the connections:
- Soldering iron w/ rosin core solder
- Heatshrink tubing
- Electrical tape

1. Take your stereo w/ panel out. I assume you know how to do this since you probably put the HU in. If not, use the beginning of this DIY.

2. Unplug the little green harness from the back of the aux jack. This is actually probably the hardest part. It's hard to get your fingers in there.

3. Strip back the tape and insulation on there about 6 inches or so. Cut all the wires, so you are left with the harness with about 6 inches of each wire. Use electrical tape to cover up the bare wires you just left hanging from the car. Strip insulation off the Yellow, Green, and Brown wires. The other wires are unused - just cover them with tape.

4. Get an RCA cable with 2 connectors at each end, or just two separate single channel cables. Don't get super thin cable or it will be a pain to work with. Cut the cable so you have about two feet of cable with the connectors on the end. RCA cable is a bit weird because it is like, insulated, then there is a layer of wire, then another layer of insulation, then more wire at the center. The wire at the center is the positive audio signal. The wire surrounding it is the ground. You want to strip off about two inches of the outer insulation. Then pull all this wire (ground wire) off to the side and twist it together. Then strip about an inch off inner wire (audio signal) insulation. Twist this wire together. Do this for both channels.

5. Put heatshrink tube over the yellow green and brown wires on the harness. You then need to twist the outer ground wires from both of the RCA channels together and then twist them to the brown wire on the harness. Twist the white plug's inner wire to the yellow harness wire. Twist the red rca plug's inner wire to the green harness wire.

To reiterate:
Yellow - Left Channel (White RCA plug inner wire)
Green - Right Channel (Red RCA plug inner wire)
Brown - Ground (Both RCA plugs outer wire)

6. Solder these connections and then heat shrink the tubing to cover the connections. Cover the three connections together with electrical tape.

7. Plug the harness back into the auxillary jack and the RCA's into your HU. NOTE: If you have an alpine head unit like I do, you will also need the KCA-121B cable to convert from RCA to the Ai-Net input on the HU.

There ya go. It looks very clean and works great!

[sgtpruitt]

Could you just splice in a Y adapter instead?

[yippieguy]

Sure you could, though you might have volume-loss issues with 2 devices plugged into the y-splitter at once...best to have 1 unit plugged in at a time if you were thinking of having 2 connected simultaneously.