(Translation of tp31207.pdf page 24, pdf page 26)

Never connect four speakers as shown in the picture.
In addition to the poor sound quality, the radio's amplifier can be damaged.
Fel! = Wrong!
================================

Rätt! = Correct!
The amplifier and speakers both have an impedance of 4 ohms. If the speakers are connected as shown in the picture, the impedance will be 2 ohms and the amplifier can be damaged.
Always check that the speakers are connected correctly.
This is done using the radio's balance and fader controls.
Always use Volvo original installation kits. Incorrect connections cannot be made and the cable lengths are correctly adjusted.
Important!
On 7601988- the speakers in the rear doors and the parcel shelf have an impedance of 8 ohms. This means that they can be connected in parallel. Check carefully that the correct speakers are used.