I have never installed a CD player (or aftermarket stereo) in a 240 without just wiring around everything. This is for 3 reasons:

1. Volvo's radio wiring sucks.
2. Volvo's amp is less powerful than the normal output from a halfway decent aftermarket unit.
3. It was the only way to really make sense of the mess.

There are different wire schemes for different model years. THe amp is in different places as well. In the 93, the amp is in the lower dash behind the little storage box. In earlier years it is under the dashboard and the storage box is bigger. I believe the 1991-1993 models had different wiring than the -1990 models. There may have been several varieties. This is similar to the 700/900 series, which shared very SIMILAR looking radios, but they are nowhere near the same. Nor are the wiring schemes between some of the years.

Ultimately, with an aftermarket unit, the best plan is often to just wire around all the garbage and chuck the amps.
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a Brickboard.com Expat