|A 1975 Austin 1300. Very popular in NZ|
Getting sales data for this period for NZ car sales is a challenge. I did manage to put this together and it gives an insight into what was going on and it was a time of great change. The NZ market had a high import duty on fully built up cars, so assembly from kits (CKD) was the only way to sell in any numbers.
In 1978 Japan became the main source of new cars, overtaking the UK where the car industry was failing due to underinvestment. For GM, the emphasis went on Holden and Vauxhall was phased out. Hillman was replaced by Mitsubishi and Honda took over from BLMC. As factories switched their source, sudden shifts in volume occurred. Japanese success also affected smaller assemblers such as VW as well.
BLMC had been the biggest company in 1975 but soon slumped as Honda profited greatly when the assembler switched to that brand. Mitsubishi's leap from 1975 to 1980 was mirrored by the fall of Hillman. The artificial assembly situation created a sudden swing to Asia as can be seen by the colours below.
One thing you cannot see in the chart was how Ford was changing too. It had been sourcing cars from the UK but was changing to Mazda cars, which started being assembled instead. Ford had recently taken a share of Mazda and rebadged some of its cars to be sold as Ford's in certain regions of the world.