Head over to clubsub.org.nz
There's a few threads on there regarding this swap, just can't seem to find them right now. There are a few different ways to do it. The cleanest way if just swapping the HU would be to cut into the HU->amp cable and then wite that to the speaker out wires on the new HU
There's another method of opening up the amp and finding the spots where the speakers inputs are soldered on and connecting it there instead.
You can potentially just buy a fascia that fits the upper half and keeps the A/C controls in place but they don't always have the brackets for mounting the new HU with them.
I just scrapped the lot in mine and did new amps and speakers aswell as the HU
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