Replacing Chorus with new Pioneer HU. Adapter trouble...


New to the forum, looks like there's alot of helpful posters!
I'm having a lot of trouble figuring out which adapters I need to connect my new HU, replacing the Chorus.

Car is an A3, 2002. There's a sub in the boot compartment. I'm not sure if the system is bose or not, and whether its rear or fully amped.
New HU is Pioneer DEH-P4100SD

I got PC9-404 connecter which I thought was correct.
And PC5-90 which looks correct.

I connected these & played around with the connections but unit wouldn't power on.

PC9-404 adapter:

Looking at the PC9-404 adapter. I don't see what it actually does, it seems like an extension as the wiring is the same at both ends. The blocks coming from the car don't match up to the input of the cable.

The red connector doesn't match up either as it only has 4 inputs where the block from the car has 6 wires. I think this means it's a bose system?

The pioneer unit has an RCA input (so red adapter can go here?) and was supplied with an adapter which takes 2 blocks input.

I've attached pictures so maybe somebody can recognise the system & whats needed?
I'd really appreciate some help!

1. 2 blocks from car system (power & L/R speakers?)
2. Block from car system to connect to red adapter & RCA
3. Adapter supplied with Pioneer HU
4. Adapter close up


Active Member
You have the non Bose system which is rear amplified (as you have front speaker connections at the HU, the brown ISO plug with 4 wires above) and you actually do need the PC9-404 adapter, but the one you have shown above is not it. PC9-404 has RCA sockets for your Pioneer rear RCA's and the other end then plugs into the 20 pin mini ISO (pic2 above). It also has a blue flying lead which then needs to connect to your remote on or power antenna wire on the Pioneer to turn the amp on. This is a PC9-404:
I've no idea what use the adapter above is as it is essentially feeding speaker outputs from the Pioneer directly into the rear amp, which you just can't do. Typical Autoleads *****.


Thanks for reply Andy.

Good to hear I have the correct connector.
From what I can see, the image I included of the pc9-404 is exactly the same as the one you linked to?

So, I should at the very least be able to get the Pioneer to power on once I hook up the car wiring to the pc9-404 which in turn connects to the pioneer adapter.

The brown ISO plug will just send front speaker connections through.

The black ISO should provide power to the HU.
But the wiring from the black connector in the car doesn't really match up with the pc9-404 connector...
Image 1 should connect to the bottom group of the pc9-404 but only the red wire & black wire at the side will connect to the brown and the red/white wires coming from car. So the yellow power wire gets nothing from car?

PC9-404 adapter

Then with the red ISO, it will take the four wires from the block in image2. But the two in the middle, orange/brown, orange/green will go nowhere.

So it looks like I'll have to do some wire snipping & rearranging or is it a case of needing yet another adapter!


PC9-404 adapter

Another thing, I just can't understand what the function of this adapter piece is! I mean, surely if you have the correct wiring to plug into this adapter (left side), it's gonne have to be exactly the same as whats on the right side of the adapter pictured? It's simply a wire extension?
Or am I missing something here...


Registered User
Some ISO conectors are separate and some are in one piece. The audi one is in 2 pieces...


Active Member
Sorry I couldn't see the image of the PC9-404 adapter. This adapter is the bit with the RCA's on it. They just include a power ISO & Speaker ISO loom to allow you to cut into rather than having to butcher the Audi loom. The Pioneer won't work because it's not getting both 12v feeds it needs, perm live for memory and ignition on to fire it up. Audi's don't use ignition on, they use the CANBUS to tell the HU when to come on, so you need to cut the yellow wire on the adapter and connect it to the red one, so that both red & yellow wires on the Pioneer are getting 12v from the single red/white wire on the Audi loom. You'll then have to turn the Pioneer on/off manually or wire in a ignition on feed from the fusebox.
With the RCA part of the adapter you need to connect the blue flying lead to the remote on or power antenna feed from the Pioneer & plug the other end into the red plug so that it corresponds to the remote on on the Audi loom, which is the white wire shown in your original pic2. This will then provide the trigger to turn on the rear/sub amp.