I was wrong. I still had all the needed wires in the Volvo harness.
It works!
Thank you very much Stu70.
All the best

I was wrong. I didn't need a wire to turn on the subwoofer. The original Volvo harness has all the needed wires.
It works!
Thank you Stu70.
All the best.

I have the original Volvo subwoofer.
I've tried to connect to the pos 2 of the Volvo subwoofer the blue/white cable coming from the Alpine hu. I made this way for the Volvo amp under the passenger seat and it works. I thought it was the same for the subwoofer amp.
Thanks Stu70.

Hi Stu70,
what do you mean with "My understanding is that D7 goes low on turn on"?
I thought that without the original Volvo radio Hu850 the wire D7 coming from the REM was "dead".

My understanding is that D7 goes low on turn on. It goes to ground (zero volts) - you would need a relay to turn this into a positive feed for your amps turn on blue /white wire. The rear d pillar speakers have a capacitor on the actual speaker that blocks the low frequencies, so you can get a ‘hig...

I've tried to connect the blue/white wire of the Alpine hu to the socket of the Volvo subwoofer (once cut the wire that come from the REM). When I turn on the Alpine I have +12V on that wire but the subwoofer doesn't turn on.
What do I need to turn it on?

Thanks.
I will try this weekend.

I've changed the hu850 for an Alpine UTE93 Dab head unit in my Volvo XC70 (Premium Sound system). I've connected the pre out of the Alpine to the amplifier under the passenger seat. I can finally listen to the radio as the original one was dead. I've lost, for the moment, the parking aid sensors: I'...