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Hello CL, long time reader, first time poster.

I love my GS: It does everything I ask. It's elegant, it's fast, and quiet. IMO, for a stock radio, the Nakamichi system sounds great and gets plenty loud enough for me. With the advent of smart-phone navigation, I don't feel any need to add a navigation system with LCD, DVD, etc. However, I would like to interface my smart-phone with my GS. IMO, the best way to do this is with Bluetooth. I thought about changing the head unit and the CD-changer. I priced it out and decided I could do a better job for (a lot) less money.

After some investigation, I settled on the GROM Audio, GROM-USB2-TOY (www.GromAudio.com). I located the Nakamichi wiring diagram from this site (thanks CL), I removed the CD-changer and reviewed the wiring with GROM, we both felt it would work. The GROM didn't work because I missed several subtle points (see my notes at the end of this note for more details). BTW, I highly recommend GROM. They have been very helpful throughout this process.

After the GROM unit didn't work, I took a closer look at the wiring for the car. I pulled the CD-changer and took a number of pictures. I have not pulled the radio -- I want to get a panel-puller before I dig into that.

I got a two-day pass on http://techinfo.toyota.com to locate wiring diagrams, etc. After reviewing everything, I believe that the Nakamichi CD-changer does not send analog-audio to the head unit. I believe it sends digital-audio. This note explains how I came to this conclusion.

To start, the wiring harness to the CD-changer has two cables:



The large white connector is the classic Toyota 7+5 audio connector it contains BAT/GND, ACC, MUTE and AVC-LAN. Note that there are only six positions wired (out of 12). I believe the signals are as follows:

• Pin 4 Mute (White)
• Pin 5 Battery (Red)
• Pin 8 Ground (Black)
• Pin 9 TXM- (Green)
• Pin 10 TXM+ (Blue)
• Pin 12 ACC (Yellow)

Note that there is no analog-audio in this connector. The smaller blue coaxial connector is the digital-audio connector.

Then, I took the CD-changer apart. All the signals were on the silkscreen.

Here's the two connectors on the back of the CD-changer.


Here are the signals in the 7+5 Nakamichi CD changer connector:

• Pin 1 CDRM Differential analog-audio negative
• Pin 2 CDLM Differential analog-audio negative
• Pin 3 Unknown I haven't found anything on this yet...
• Pin 4 Mute
• Pin 5 Battery +12V
• Pin 6 CDRP Differential analog-audio positive
• Pin 7 CDLP Differential analog-audio positive
• Pin 8 Ground
• Pin 9 TXM- AVC-LAN bus negative signal
• Pin 10 TXM+ AVC-LAN bus positive signal
• Pin 11 Signal Ground For use with 1,2, 6, 7
• Pin 12 ACC Accessory voltage

A few notes on all this:

1. It looks like the CD-changer itself has analog-audio output. But instead of using that, Lexus opted to use the digital-audio interface. It's a good decision. If the digital-audio link works, no electrical engine noise will leak into the audio system.
2. The digital-audio interface cable is taped on to the main CD-changer wiring harness. To me, this indicates that this wasn't the original design. If the plan all along was to use the digital-audio interface, they would have put all the wires into the same wiring harness.
3. There are no analog-audio wires in the CD-changer wiring harness. Again, to me, this indicates that some of this change was done upstream of the assembly plant (i.e. the wiring harness was intentionally built without the audio wiring).
4. I found this picture from a different CL post. Here's a link to the post: https://www.clublexus.com/forums/gs-...anger-pin.html. This connector is wired exactly the same as mine. It's not clear from the post if the poster was trying to do. But whatever he was trying to do, apparently it worked. Is this connection common?
5. What did I miss? Why didn't the GROM GROM-USB2-TOY work?
   1. I thought that the D-6 connector in the TIS Nakamichi stereo diagram was a Toyota 7+5 connector. It isn't. The D-6 connector is really a 14 pin connector. But, it is very similar to the 7+5 and it's in the right location to be this 7+5 connector. This is a bit of a mystery. There is no 7+5 connector on the TIS Nakamichi stereo diagram.
   2. I missed the fact that there was no analog-audio in the CD-changer connector.
   3. For some reason, the GROM wasn't detected by the head unit. I'm not sure why.
   4. There's more, but any of the above would be sufficient.
6. Last, and I most significant is that I cannot find the Nakamichi CD-changer audio connector (the 7+5 connector) or the blue coaxial digital-audio connector on the TIS Nakamichi stereo wiring diagram for the 1999 GS400. I am going to put my notes on that subject into a different post.

For those interested, the PDF has all the same information and a little more...