Nakamichi low volume

[Exhaustgases]

1990 Ls, it had a phone so I suppose it may have something to do with it. The phone transceiver box is fully disconnected, funny how they did so many different installs of the phone systems, seems like no 2 are alike. This has no driver controls, and had a goofy mount in the box that doesn't look like others I have seen.

[1990LS400]

All official Lexus branded dealer installed phone systems had a controller on the left side of the steering wheels and the word "Lexus" on the handsets.  The handset cradle on Lexus branded phone systems plug into factory connectors under the rear of the center armrest.

The original Lexus branded phone system was pricey.  When I bought my first LS400 in 1990, the phone system was around $1,000.  I instead bought a much less expensive President-brand phone system through the Lexus dealer that looked very similar to the OEM system but did not have steering wheel controls or use any of the factory phone pre-wiring.

Assuming that yours is an aftermarket phone system, look to see if its wire harness includes a yellow wire.  Audio mute wires in aftermarket phone systems are almost always yellow.  If you find a yellow wire, trace it to see if it connects to a wiring harness on your car.

Some aftermarket phone system installers connected the phone system's audio output wires so that it plays the call through one or more of the car's speakers but most use a separate speaker for the phone audio.

There weren't all that many Lexus branded phone system versions used in the LS400 - four or five in North America during the 11 year run of the LS400.

[Exhaustgases]

On early 90's Ive seen this same set up and what you say too about that control at the steering wheel. This one must have been the cheapy dealer one then. I tried tracing them a while back when I did the climate lcd it went deeper than I wanted to go at the time.