Installing a head unit

You have 2 sets of wiring. The HU loom, and the car loom.

Ok, the HU loom. This is made up of the wires;

Red – Switched Live
Yellow – Permanent live
Black – Ground.
Blue – Remote
Blue with white stripe – Electric aerial

The Blue and white wire is only on certain HUs, as the remote wire gives out 12V so is often used for an electric aerial and/or amps.

The Permanent Live is just that. It should have 12V to it whether the car ignition is on or not. This should be fused if you have to put one of these in, as some cars are not built to take head units.
The switched live should be live when the ignition is switched on, and there should be no power at this wire with the ignition off.

The speaker channels…….
White with grey stripe – Front Left
Grey with black stripe – Front Right
Green with black stripe – Rear Left
Violet with black stripe – Rear Right

Obviously, when wiring up the speakers to the HU, you need to keep some sort of consistancy. The speaker wire is likely to have something written on one side of it, use this as the positive side. The HU, when you look at the back, with the wires coming out of it, use the right hand side for instance of the two matching colours as the positive side. This will ensure you wire all the speakers to the HU in exactly the same way, meaning all of the speakers should be in phase. This matters a lot.

Ok, at the car loom side……..
Every car will have different colours of wires coming from the car loom. If you have a manual, it might have something about the wires, or indeed a wiring diagram for them. If not, you will need a test lamp, or a voltmeter.

You need to bare the wires and keep every wire seperate. I cannot emphasise the need to keep all of them away from each other, and don’t turn the ignition on until you are happy.

You need to be testing for the power wires, and the earth wire. It is possible that these wires are seperate to the speaker wires as quite often they are loomed up seperately.
Take the test lamp, and look for a power wire without the ignition on. There should only be one that is live without the ignition on. This is the permanent live and should be connected to the Yellow HU wire.

Next, turn the ignition on. You should now find another wire that is live. This is the switched live wire (you can test by turning the ignition off, and this will now lose the 12V feed) and should be connected to the Red wire on the back of the HU.

The earth wire will be of the same gauge (thickness) as the 2 power wires. It will also be likely a plain dark colour, either black or brown. The speaker wires will likely be in pairs also, so it will leave one wire without a terminal, this is likely the earth wire.

To test the speaker channels……….
You can test the speaker wires by using an AA battery. Connect the wires to each end of the battery. When you get some noise through the speaker, you have found a pair of speaker channels.

The other way, and best way i find, is to turn the HU on, and fade the speakers in turn. So, fade the speakers to the front, and then say the left. This means, you will only get noise from this speaker. Now, take the pair of White with grey striped speaker wires, and touch them to the speaker wires in the car loom. When you get the noise through the front left speaker, you have the right combination. Now do this for all the speakers in turn. Try to keep the continuity though, by using the stripes on the speaker wires or some writing or something to keep you wiring them up the same way.

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