Well after a lot of mucking around I narrowed it down to one model that was not displaying bright lights.
The model "New Zealand Police 2013 Holden VF Commodore SS Highway Patrol" by Donnzy for some unknown reason, only has dimmed light bars on the cars with the red highway patrol markings. As the same model is used for the marking DDS files, it's beyond me why it happens.
Only way I could have all cars with bright bars, was to use his car "2017 Holden VF Commodore Series 2 SV6 - NZ POLICE HIGHWAY PATROL" for the police3 slot.
I'm also using it in the sheriff slot (it's original located slot) and it's all working OK.
There's only one vehicle left in the game that I'd like to change. That's the police transporter (slot policet ). If anyone can point me to a good NZ replacement I'd be grateful (if there is one)