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ISO wiring for the 75’s

The random wiring in the 75 for the stereo has always annoyed me.  The wiring is messy enough already the way it is inclined to hang loose; and let’s face it; I don’t really want a radio-cassette (!) player any-more.  I want MP3.  I  want Bluetooth.  I want USB and iPod.  And I want it NOW!
As most/all stereos available nowadays are wired for ISO connectors, I end up butchering the supplied connector and kludging another set of wires to hook into the new stereo, just making a bad lot worse.
So I end up with this work of art:

Rats' nest

The really weird thing, to me, is the allocation of the different wires to their different connector blocks; it obviously dates back to the time of “front speakers only”, as all the power, ground and front speaker wires are in one connector block (the eight-way one).  The rear speakers meanwhile get their own six-way connector. 
Even here the layout seems deliberately odd as you can see from the pic above.

The ISO layout

Now the ISO layout is, as you would hope, a lot more logical than this, with two discreet connector blocks, one for the speaker wires; the other for the power and ancillary connections.  The ISO wiring layout is shown here:

ISO Wiring

And it's trying to mate with this

Alfa75 Wiring diagram

What to do?

Well the question was, how to improve upon this amateurish approach that I had been using to date? 

I found this interesting item on eBay "PC2-03-4 Alfa Romeo 155 164  ISO Lead" - from http://stores.ebay.co.uk/liquidice-2008.  Yes I know this is for the 155/164, but bear with me.  This vendor also lists a lead for the 75 specifically, but this is simply a straight-through male-to-female ISO to ISO lead, so is particularly useless for anything other than lengthening your stereo’s existing ISO lead.  Eh, yeah!
But, but, but.  Look at this"PC2-03-4" thing; it’s got the same connectors as the 75, just with some re-arrangement of the wires.

155 connector

It seems that Alfa weren’t so thick after all.  On the 155/164, it appears that they have gone pseudo-ISO in that the wires are here separated into the two logical blocks.  All the speaker wires go to the 8-way block, and all the power & ancillary wires to the 6-way.

Note: I don’t have either a 155 or a 164, so I’m basing the above on the lead supplied in the pic above.  Perhaps someone with one or the other could confirm?
So the only question left was, “Do I alter the 75’s wiring blocks to accommodate the pseudo-ISO setup, or do I change the lead above to mirror the 75’s way of doing things?”  Well, perhaps the easiest answer is – “I’ve got two 75s

I can faithfully report that both methods work equally well.
While I was at it, I also decided to run two other signals to the 75's connectors that  are represented on the ISO connector, but missing from the originals; namely a switched-power and a dashboard illumination signal.  The switched power I took from pink/white wires behind relay I48 on the main fuseboard.  The dash illumination I took from the black/white wires behind the heater console.
Extra signals
Ignition-switched power

Why bother?

Well, obviously I could have just bought in the connectors, and lots of terminals, and lots of spools of nicely coloured wire and made these things up myself.  Alternatively I could have left well enough alone, with my butchered connectors and the labels on each cable to remind me what's what next time around.  But this particular lead is well made, the connectors all professionally finished and, even better, each of the wires has its function printed on it.  So no more labels to mess with.  And they're pretty cheap, all things considered.  Well worth it in my opinion.

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