Any truck mechanics about that can help me please?

The radio in my 06 Daf 85 cf has stopped working, literally just wouldn't turn on one morning. I swapped the whole headunit out and still nothing so I got the multimeter out and had no power at the stereo, removed all my parrot kit too, still nothing. Got power at the relay in the fusebox but nothing at the headunit end. Is there a power inverter on these? I've taken the dash panel off and traced the wires ( I think ) to infront of the heater box and I didn't go any further. It's been broken for about 3 weeks now and im more than a bit bored of it tbh :-/ it's up for MOT next month anyhow but would like a bit of background noise before then I'm going slightly mad

Cheers. Joe