The items that fit your Porsche Boxster (986) are shown below.

Porsche 911 (996) and Boxster (986)

Production years 1997 - 2004

1997 to 2004 model Porsche 911 and Boxsters have two original audio systems.

The earlier cars had a system similar to an Audi, the speakers are amplified and the head unit suppliers the audio to the amplifier via a low level signal from the Mini ISO connector. These cars require high to low level adapters to fit new head units or handsfree kits.

Later models use a fibre optic network to send the audio signal from the head unit to the amplifier. For these cars we have the 23-245 fibre optic interface available.

Generally the CD22/CDR22 original units have the Audi style system, CDR23 units can be either low level like the Audis or fibre optic. It is best to either find the amplifier under the front bonnet and look for fibre optic cables, or remove the head unit and look at the connection on the back.

Here is a picture of a car using a low level signal in the Mini ISO yellow connector to connect to the amplifier, note that all six positions are populated. These wires are the positive audio signals for front left, front right, rear left and rear right speakers, a common speaker negative and the amplifier turn on signal. Models with this set up will need to use the 20-281 amplifier interface.
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Here is a picture of a head unit using the fibre optic connection. Note that there are only four wires in the yellow Mini ISO, unlike six in the older version. These four wires are data wires, they do not carry any audio signal. Models with this fibre optic system require our 23-245 fibre optic amplifier interface to work. This not only connects to the amplifier but provides a switched live direct from the fuse box.
 

There are some cars with the very basic audio option, these have a traditional speaker ISO connector with the head unit driving the speakers directly. No audio adapters are needed for these cars.