Thanks Titus,
I checked the area as you suggested and found 24V to pin 19 of the VMC 20 master controller (this wire is the sense wire for the parking brake application switch.) I did this by backprobing the pin 19 on the multiplug. I would like to extract the pin to confirm the 24V is coming from the wire and not internally, where can I get the release tool and pins & sockets for this style plug? It is a Tyco style I believe, same as found on Linde trucks with a coloured release bracket that slides out of the side of the plug and ramps the plug out of the socket.