"Wiring A Punto Stereo To Ignition Using ISO" (yellow red wires) MK2 only not MK2b

So basically, if you have a Punto like mine (mine's a 51 reg with the 6 speakers+subwoofer system), you will have an ISO connector in two parts, a white part and a black part. The black one is for the speakers, the white one is for power + control signals.

On the top row of the white one, pin 3, is a green and blue wire. This is an ignition switched power connection (as shown in the Haynes manual, and which I confirmed by testing with a multimeter). It is wired through the 7.5A fuse F49 in the interior fusebox. Here is a pic showing the wire:


I connected this to the "switched power" input of the radio. Your colours may be different, but if it's like mine (Pioneer DEH-5000UB ... nice head unit by the way) then the connections are:
Car black (pin 8) --> Radio black (battery negative)
Car red+white (pin 4) --> Radio yellow (THIS IS THE PERMANENT POWER)
Car green+blue (pin 3) --> Radio red (THIS IS THE SWITCHED POWER)

To do this I used a paperclip to pop pin 7 (red wire) out of the ISO socket on the loom that came with the stereo, and poked it back in so as to magically become pin 3, before connecting it to the car. (So no modification to the car wiring was needed, which was nice.)

Here's a pic of the red wire ready to be poked back in to slot 3, to live in its new home above the yellow wire:

I was worried the 7.5A fuse might not be enough, so before I did all this I measured the current drawn by the head unit and it turned out it takes hardly any current from the switched wire anyway (my crappy £2.99 multimeter showed 0.00A, so less than 0.01A... :)). Rather, all the current used to power the radio is drawn through the permanent connection. The switched connection seems just to be used as a signal line. This wasn't surprising, since the yellow wire on the loom is big and thick while the red one is quite thin at the head unit end. (All this might not be the case on other radios of course so I would advise checking for yourselfl!!)

So anyway, it's all working lovely, and I'm glad I didn't need to dismantle the steering column and splice the orange wire (although it would have been fun!) Hope this helps.