OK, poking around with a multimeter set for dc volts ;
Pin 7 to Pin 4 & 5 (common) - 48 V
Pin 8 to Pin 4 & 5 (common) - 48 V
So looks like Mode B PoE. Looking at wikipedia Mode B, T568B color schematic, RX+ is on pin 1, and RX- on pin 2, and as you mention, pin 1 & 2 can't be common.
As its only six wires, and it would be obvious that you could common 4 & 5 and 7 & 8 onto one wire each, and then I noticed that the wires I currently had on 7 & 8 matched the T568B colour scheme for RX+ and RX-, it looks like I had 1 & 2 (purple) and 7 & 8 (orange, white/orange) transposed.
Swapped them over, and all working now.
Hence, the correct wiring for this cam is ;
Pin 1 - white wire with orange trace
Pin 2 - orange wire
Pin 3 - Green wire
Pin 4 & 5 common - grey wire
Pin 6 - white wire with green trace
Pin 7 & 8 - common, purple wire
Pic below ;
View attachment 9183
Thanks for the pointers on pins 1 & 2, and that the solder pad number don't necessarily correspond to the RJ45 pin numbers