@Phaedrux
When I went to connect the 4-wire cable I had to first disconnect the flat cable so I could turn the printer on it's back to access the Mini-5.
I removed the flat cable from the Mini-5 and took at look at the connector. All seemed good so I reconnected it.
I realized after looking at the Mini-5 I didn't have the right 4-wire cable.
So I put the printer back on it's feet, reconnected the PanelDue and powered the printer up.
The PanelDue connected without issue - something to do with disconnecting/reconnecting the flat cable perhaps.
Thanks.
Frederick