My newest 240 is 1988, things may have changed in later wiring.
One type of wiring ends up with the car wiring supporting the trailer lights; a better type has the car wiring tripping a relay which then sends voltage from the battery to the appropriate trailer light.
The second type does not add the trailer light load to the bulb failure warning system relay. It will take more time and effort to install.
I do not know which type the Volvo system provides but being designed by Volvo it should be a good one.
Download and use the Volvo instructions anyway, you will get good diagrams and instructions (in six languages) for whatever system you select.
Good Luck,
Bob
:>)
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