Thanks everyone for the contributions - I am narrowing down the possibilities, but am now stuck again as I don't know enough about the standard X5 wiring for a car produced 08/01.

I have confirmed that I have audio present on the ELK 800 amp outputs as required. I have confirmed that this audio signal transfers to the white X400 (is this the correct term?) plug on the existing main car loom. To my mind, this suggests that the problem lies between this point and the speakers, which leads me to think either:

1 - The connection is not already made in the standard car wiring; or

2 - There is a fault with the wiring.

I have tried to test for continuity with pins 3 and 8 of the plug which incorporates the CD changer inputs to the back of the radio unit under the spare wheel (thanks John and UcrewX5 for your info - vary helpful) - but can't find any continuity with the output from the amp, making me think there is a problem with the wiring.

Question 1: The plug incorporating the CD changer inputs to the radio (is this plug x13321 or x01037??) appears to run straight to the back of the CD player, with only 4 wires present - where are the other two which go to pins 3 and 8 for the + and - Telephone Audio Inputs (i.e. where are they supposed to join in the loom)??

Question 2: On cars with Nav, are there any other connections not made which I need to plug in (in the same way as referred to in the technical service bulletin for cars with no Nav)?

Question 3: Does anyone have a wiring diagram showing how the white X400 plug audio wires connect into the audio inputs on the radio?

Very grateful for any input anyone can give - I am sure I am not the only one who has had these problems.

Best regards,

Jeremy.