So i've been reading up various threads on how to add an aux input to the pre 2003 factory system by hacking into the tape deck outputs. Here's my write up:
With the Sat Nav removed (remove plastic surrounding trim then 4 small screws - 2 in the top and 2 in the bottom) you can see the 2 harnesses plugged into the back:
The blue one is the one we are interested in since it has the audio outputs and power feeds. The photo below shows the 2 pairs of twisted wires - yellow and blue which are the audio outputs from the Tape Deck. The Yellow is the Right channel and the Blue is the Left Channel.
To remove any interference from the tape deck itself I cut the output wires completely and attached them to RCA cables:
Now the output of my Iphone needs a boost to enable the sound level to be similar to the radio and CD changer - so I used a Line Driver. The sequence is:
Iphone------Line Driver------Tape Deck Outputs
In order to power the Line Driver I spliced into the power and ground on the blue harness:
The Red wire with green trace is the permanent live and the purple wire is the switched live (only turns live with ignition) which goes to the remote input on the driver. The Ground is the brown wire.
With the line Driver wired in I used a Headphone jack to RCA cable to feed it from the Iphone:
The driver gain was then turned up to almost maximum and then tucked away inside the sat nav cavity. I routed the aux cable through the cup holder and left it long enough so that I could comfortably control the iphone:
With everything ready it was time to test the sound. I used a normal tape in the deck to fool the system - I didn't bother with a dummy tape as I had cut the output from the deck anyway.
The sound was pretty good - volume level was very close to the radio and CD changer and it had good bass and treble tones. I found the best sound was with the Iphone EQ settings turned off - or flat.
Out of curiosity I also had an AV cable which plugged into the base of the iphone. So using the RCA audio outputs of the cable into the line driver - i tried this method. However I found that this produced a more muffled sound where the treble tones seemed to be lacking. This could be because I was using a cheapo cable? Anyway - I reverted to the headphone output of the iphone and I have to say I am pleased with the performance.