Adding Central Locking on Habitation door

[alanwdk]

My 2018 Bailey is based on a Peugeot Boxer chassis. The cab has central locking, but the habitation door is not linked. I have a 5 wire central locking motor which I can add to the door and bring wires to the cab - but wondering where is best / how to connect it to the existing central locking ? Any help appreciated.

 

[Clivefog]

I'd piggy back it onto the cab door motor wiring