Brera stereo change - Alfa Romeo Forum
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Brera stereo change

Hello all,

So I have bought a brera in the last few months and have been loving the car other than the stereo, I have a head unit that I have taken out of one of my other cars to put in there.
So I changed the stereo (using a harness adaptor) and there is no sign of life in the head unit, so I plug the factory unit back in and it works perfectly.

Any ideas on why the aftermarket unit doesn’t work and the factory unit does?
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(Post Link) post #2 of 10 Old 3 Weeks Ago
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If it was live in the old car then the harness is the problem. But also note that the original unit sends power to the aerial to get a signal.
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Have you checked that the wiring in the harness adapter is the same? or the pins are making contact - they're not always made to the same standard as the wiring in your car. Most wiring harnesses have a red and yellow switchable wire as not all +ve and ignition +ve are in the same location.

Also worth a check, some head units have a small 10A mini fuse on the back, somewhere around the wiring plug - never seen one go before, but I suppose it's possible.
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Well the stereo works, it has been tested and working in another car, so as you say, probably the harness at fault here.

I did try the old swapping the yellow and red connectors over and didn’t have any joy. Just wondered if there was some funny Alfa thing that I hadn’t thought of before I blamed the iso harness.
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Quote:
Originally Posted by SketchYDG View Post
Well the stereo works, it has been tested and working in another car, so as you say, probably the harness at fault here.

I did try the old swapping the yellow and red connectors over and didn’t have any joy. Just wondered if there was some funny Alfa thing that I hadn’t thought of before I blamed the iso harness.
There's a couple of things.....

- the standard HU on/off is controlled via the CAN bus, so often on the Alfa's there is no switched +12 present in the ISO loom. Also permanent and switched +12 are often interchanged in the Alfa loom .....
(ISO A4 & A7)

- If you have Bose, you need to supply the amplifier switch-on signal, otherwise no sound.....
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Originally Posted by jwq View Post
Quote:
Originally Posted by SketchYDG View Post
Well the stereo works, it has been tested and working in another car, so as you say, probably the harness at fault here.

I did try the old swapping the yellow and red connectors over and didn’t have any joy. Just wondered if there was some funny Alfa thing that I hadn’t thought of before I blamed the iso harness.
There's a couple of things.....

- the standard HU on/off is controlled via the CAN bus, so often on the Alfa's there is no switched +12 present in the ISO loom. Also permanent and switched +12 are often interchanged in the Alfa loom .....
(ISO A4 & A7)

- If you have Bose, you need to supply the amplifier switch-on signal, otherwise no sound.....
No Bose system so don’t need an amp bypass harness.

With the on/off being controlled by the can bus, would I need to also have a steering wheel control adaptor to have the head unit turn on via can bus signal? (If I understand correctly the steering controls are done by can bus as well)

If it Ain't broke, fiddle with it, break it, fix it, upgrade it.
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Originally Posted by SketchYDG View Post
No Bose system so donít need an amp bypass harness.

With the on/off being controlled by the can bus, would I need to also have a steering wheel control adaptor to have the head unit turn on via can bus signal? (If I understand correctly the steering controls are done by can bus as well)
No, you can simply add a switched +12 tapping into the wire for the cigarette lighter for instance.....
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No, you can simply add a switched +12 tapping into the wire for the cigarette lighter for instance.....
Where would I need to pull the permanent +12v from? Or is the +12v in the harness and I just need to run a cable for the switched 12v?
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Quote:
Originally Posted by SketchYDG View Post
With the on/off being controlled by the can bus, would I need to also have a steering wheel control adaptor to have the head unit turn on via can bus signal? (If I understand correctly the steering controls are done by can bus as well)
Ah, I assumed that's what you meant by the harness! unsure what you're using as the standard plugs on the car are the ISO ones, and should fit directly into any modern stereo's wiring - they just won't work.
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Where would I need to pull the permanent +12v from? Or is the +12v in the harness and I just need to run a cable for the switched 12v?
Permanent +12 should be in the standard ISO harness, as this is also used with the CAN bus version, either in A4 or A7. It's just the switched +12 that's probably missing, as this is not needed for the CAN version.

Normally on a standard HU, the permanent +12 will be connected to the yellow wire on the HU, switched +12 should be connected to red wire.
As said, these are normally on ISO A4 and A7.

Standard ISO would be A4 = switched +12, A7 = permanent +12. But as said, on Alfa could be exchanged, and switched +12 could be missing.

Often on HU's, the red and yellow wires have bullet connectors in the wires, so you can simply cross them over if required......
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