Wiring diagram of the DSP amp, showing which wires go where and what each of the 3 connectors do.

Mines a Facelift 2004 model, 4.8, with widescreen satnav and subwoofer.

The pinouts for the 15 pin connector (X18771 - Black Connector) are:
PIN - CONNECTION
1- Sub 1 +
2- Sub 2 +
3- LH Rear loudspeaker - (Touring LH rear speaker ground) YELLOW
4- Radio on/antenna signal
5- RH rear loudspeaker + (Touring RH rear +) BROWN
6- Sub 4 -
7- Sub 3 -
8- Terminal 30 connects to Fuse 56
9- Sub 1 -
10- Sub 2 -
11- Touring LH rear + BROWN
12- Touring RH rear - BLUE
13- Sub 4 +
14- Sub 3 +
15- Terminal 31 connects to Ground Point


The pinouts for the 18 pin connector (X18772 - Black) are:
PIN - CONNECTION
1- Not used
2- Low freq. negative (-) signal - Transceiver/charging electronics
3- Not used
4- Not used
5- I-bus Signal Line - Splice X18344
6- Not used
7- Not used
8- RH front speaker - Connects to Radio
9- LH front speaker - Connects to Radio
10-Not used
11 Low freq. voltage (+) signal - Transceiver/charging electronics
12-Not used
13-Telephone mute signal - Transceiver/charging electronics
14-Not used
15-Telephone ON signal - Transceiver/charging electronics
16-Not used
17-RH front speaker + - Connects to Radio
18-LH front speaker + - Connects to Radio


The pinouts for the 26 pin connector (X18773 - Blue) are:
PIN - CONNECTION
1- LH front woofer + BLUE+WHITE
2- LH front woofer - BLUE+BROWN
3- Not used
4- RH front mid-range - BROWN
5- LH front mid-range + BLACK+GREY
6- Not used
7- Not used
8- Not used
9- RH front mid-range + BLUE+YELLOW
10-LH front mid-range - BROWN+GREY
11-Right rear mid-range speaker/tweeter + BLACK+WHITE
12-RH front tweeter + BLUE
13-RH front woofer + BLUE+RED
14-LH front tweeter + YELLOW+RED
15 LH front tweeter - YELLOW+BROWN
16-Left rear mid-range speaker/tweeter - BROWN+YELLOW
17-Not used
18-Not used
19-Left rear mid-range speaker/tweeter + BLACK+YELLOW
20-Not used
21-Not used
22-Not used
23-Not used
24-Right rear mid-range speaker/tweeter - BROWN+WHITE
25-RH front tweeter - BROWN+BLUE
26 RH front woofer - BLUE+BROWN

The number of speakers are:
2 in the rear door cards = 4
2 in the front door cards = 4 (up higher near the outside mirrors)
2 in the dash up high (base of the windscreen)

Highlighted in Bold are the ones you will need to tap into. I have also included the colours.
Essentially, if looking at the car from the back you will need to tap into the following from the 26 pin connector:

Front Left (Passenger):
Tweeter - 14, 15
Mid (in Dash) - 5, 10
Sub - 1, 2

Front Right (Drivers):
Tweeter - 12, 25
Mid (in Dash) - 4, 9
Sub - 13, 26

Rear Left (Passenger):
Tweeter/Mid - 16, 19
Sub - 3, 11 [15pin Connector]

Rear Right (Drivers):
Tweeter/Mid - 11, 24
Sub - 12, 5 [15pin Connector]