Note: the solenoid text in the image is just a representation.
Real world everything is fine until I connect the solenoid to the Com and N/O of the relay. It then cycles once and starts to continuously re-trigger on it's own once a second or so. I disconnect the solenoid and it works as it should.
I have used the common 12V as in the image and I have also given the solenoid it's own separate 12V but it makes no difference.