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Head unit modification on a 1999-2005 Saab 9-5 to add a line input for external media player connectivity.

Parts of this guide are outdated, please search Saab forums for more recent solutions for adding a line input to a 9-5. You can still use this as a general guide on taking the stereo apart.

A digital music player is an attractive and convenient source of music in the car, but the stock head unit does not have a line input. Many people end up using an FM modulator or a cassette adapter, which inevitably sacrifices the sound quality. Not everyone agrees to this compromise, especally if you have a premium Harman Kardon stereo in your car, or a custom upgraded system.

There are several alternative solutions for direct MP3 player connectivity. This guide shows how to do it yourself by using the tape deck inputs of the internal amplifier. It is a relatively easy and inexpensive way to add a direct line input to your stock head unit without sacrificing any existing functionality.

Thanks to Daniel Giertz and all the Saab forum members who did the research and contributed to the installation guide.

Stereo removal

Remove the head unit from the car. If you don't have a stereo removal tool, use a set of knitting needles, or just four long nails. Stick them in and pull the stereo out.
Mounting case

Press the sides of the mounting cage inward to release the latches and pull the cage out. Detaching the wiring harness from the back of the cage will make it easier to test the unit later.
Head unit

The face panel of the head unit is held by four Philips screws (two on each side) and hald a dozen plastic latches.
Front panel removed

Unplug the front panel. The top cover of the CD player module is not necessary to remove, but it's easy to pop if you're curious what's inside.
CD player screws

The CD module is secured by three Philips screws.
CD cable

Before removing the CD module, unhook the ribbon cable from the main board.
CD module

Lift the CD player module and store it away.
Tape module

Unscrew the tape player module (4 more screws). The little vertical board on the right side of the module is plugged into the main board. Unplug it with care.
Head board

These two green jumpers lead to the stereo signals from the magnetic head. I haven't noticed any feedback or distortion with the circuit uninterrupted, but it's highly recommended to unsolder these jumpers to disconnect the tape signal amplifier or install a switch to alternate between the deck and the aux input.
Stereo signal

Connect the external stereo wires to the connector leading to the main board. Ground is pin #1, right channel (red) is pin #2, and left channel (white) is pin #3. Some head units (AS2 vs AS3) have a different board layout, but the pin-out of the connector is always the same.
Tape control board

The tape control board carries the signals from various tape sensors. The load switch ("LOADSW") in the top right is a switch that gets pushed when the cassette goes in. The front and rear reel signals ("FRS" and "RRS") are the rotation ticks from the tape spindles. And the "INT" signal initiates the head engagement.
Signal taps

First, tap into the load switch line. Grounding it tells the deck to load the cassette tray. Shorting the front and rear reel signals will fool the control logic into thinking that both reels are spinning (the downside is that it will effectively disable the tape jam protection). Finally, solder a wire to the resistor leading to the "INT" pin.

You can opt for an external switch, but I chose to install these two for a completely stealthy setup. Note that the one on the right engages first, and the left one only clicks when the tape door is at the end of its travel. Both switches are normally open, closing them shorts to ground (find a local ground source on the face panel board).

Connect the first switch to the "LOADSW" signal, and the second switch to the "INT" signal. If you're careful enough, you can even position the switches so they are not engaged when a regular cassette hits the door, to preserve the cassette playback functionality (sans the jam protection).

Connect the MP3 player and turn the stereo on. Push the cassette door inward to hit the first switch. The stereo will switch to the tape mode. Usually, the deck will start right on and show "TAPE PLAY A>" (or "B"), playing the music from your MP3 player. If you only see "TAPE" on the SID, push the door further to press the second switch for a second or two, then release it. The deck will engage the playback and you'll see "TAPE PLAY A>".

Re-install the CD player module and put the head unit back into the car. Route the auxillary cable to a convenient location of your choice. Enjoy the music. If you find the tape suddenly switching to "FAST FORWARD" after a few seconds of playback, disable the fast seek feature by pressing the middle of the "SEEK" button on the head unit.

I attached the stereo plug to one of the dashboard blanks.

The tiny mobiBLU player fits directly onto the stereo jack and looks right at home at this location.

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