Autosleeper Pollensa 12v Fridge in/op

Traced fault to alternator signal voltage missing at fridge relay. Checked signal voltage output from alternator which is ok. I have lost the voltage on the wire between the alternator and the fridge relay. I have traced the relevent purple/black wire into the main wiring loom but from there on I can only find it then at the fridge relay. Has anyone had this fault before? Does anyone know if there is a connection point between engine bay and the interior?

Thanks