I used to run a couple of Strathfield Car Radios workshops for about 4 years back in the day and am happy to help out. To give the best advice, it's best if I see photos of exactly each issue..
Wiring harness: Aerpro are the main company in Australia that makes & sells stereo head unit wiring harnesses, see if they have what you want, they are sold in many outlets like SCR, Auto barn, Supercheap Autos, etc, and could order it in for you:
Harnesses - Car Audio Accessories AERPRO
Blue wires: There are usually 1 or 2 BLUE wires coming out of a NEW stereo wiring harness, which are for a) signalling an amplifier to switch on (the whole time the stereo is on), and b)switching on a small antenna signal amplifier (which only gives out a positive signal while the radio is on).
The only problems I've seen with using a wiring harness are usually just the two positives needing to be switched around sometimes. So the Yellow and Red wires, which are Constant Positive, and Accessories/Ignition Positive respectively. If your radio won't save radio stations or any other settings, these two wires need to be swapped. You can just pop the pins out, swap them over & pop them back in.
Also, the best method for keeping the wiring in place to put the original head unit back in is to just 'tap in' to the original wiring harness, don't cut it off. Then, when it's time to re-install the original Head unit, just cut off the 'new stereo' wiring from where it was attached to the original car wiring loom, and tape up neatly the stub of solder left behind..
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