Clicking noise; lights and blower work intermittently

[LordSandwich]

I have an issue with my mk7 van. when the ignition is on, there is a clicking sound, and the lights and blower will work intermittently, if at all. I had the BCM under the glove compartment replaced with the "high level" module about a year ago, in order to activate cruise control. Could this be the reason why it's not working?

[Altransit]

Possible intermittent failure of the ignition switch, and have you checked the state of the battery (or batteries), and their connections

[LordSandwich]

The van belongs to my Dad, who I'm helping to convert it into a campervan. So far, I have replaced the ignition switch, and he has cleaned up the battery terminals, as well as (I think) replacing the front battery. I know that he connected a solar panel and some leisure batteries, but I think he has since isolated that system from the main batteries.