New Head Unit
 

Just bought a 2003 C70 and I've replaced the standard Volvo unit with a Pioneer double din unit.

I've got the connection kits with the RCA to DIN plug - Cut a long story short, everything looks to function perfectly, however there's no sound - I'm fairly convinced I need to connect the little blue wire to something in order to tell the on-board amplifier to turn on.

Can anyone tell me where this needs to connect to please, or indeed something else I'm missing.

Thank You https://www.ebay.co.uk/itm/Volvo-PC9...-/181255407145

The DIN to rca adaptor should have a single lead coming out of it, and four rca plugs.
The lead coming from the amp in the rear of the car, is connected to the adapter, the RCA leads go to the new radio. Make sure they are on outputs not inputs.
The radio should have a lead , labelled something like remote, possibility blue, that is for
Turning on the amp. This goes to the single lead on the adapter.
I hope this helps, if you haven’t already done it.

Roger.