Before the ambulance arrived, the injured man died .
No need for past perfect here.
As the ambulance approached the scene, the driver noticed that no one at all was attending to the injured man. This was because, before the ambulance arrived, the injured man had died. No one was looking after the injured man, because he had died.
Past perfect is needed as explanation but the sequence of time without it would be crystal clear. Would it be possible to use past simple?
My dad was furious because I scratched his car.
So why not past perfect for scratched as it is an explaination of why my dad is furious?