Main Unit

Main unit inputs







- Power supply +15 (20)
- Power supply +30 (1)
- Ground (G42)
- Telephone mute (375)
- Telephone, line input +/- (375)

Main unit inputs, bus







- Ignition +B (on/off) from DICE (628)
- Steering wheel switches from SID (541)
- Key Correct from TWICE (632)
- Diagnostics communication, see Bus and Diagnostics communication.
See Powertrain Management/Computers and Control Systems/Information Bus/Description and Operation/Diagnostics Communication

Main unit outputs







- Mute control, external amplifier (354)
- Line output, right/left channel +/- (front/rear) (354)
- Speaker, right/left channel +/- (front/rear) (266)

Main unit outputs, bus







- Sound (sound information) used by SID (541)
- Text message (text information for main unit) used by SID (541)
- Diagnostics communication, see Bus and Diagnostics communication.
See Powertrain Management/Computers and Control Systems/Information Bus/Description and Operation/Diagnostics Communication

Main unit







General
The main unit for the telephone system is the audio system main unit. It is connected to the wiring harness and the bus via a 26-pin connector.

The main unit performs the following tasks:
- Disconnects the normal sound from the selected source during a telephone call. This is achieved by sending a mute signal to the main unit, which then disconnects the normal sound to the speakers and the signal to the external amplifier where relevant.
- Receives the audio signal (line input) from the telephone (incoming sound) via the telephone contact and reproduces it via the audio system speakers.
See Test readings, control module connections

Main unit power supply












Power supply (+15 circuit)
From fuse 21 to the main unit, pin 2.

Power supply (+30 circuit)
From fuse 9 to the main unit, pin 8.

Main unit ground







Ground connection







The main unit is grounded (main ground) at grounding point G42 (LHD) or G40 (RHD) via pin 4.