In the post #5 photo the clear LED at the bottom of the PCB is a sensor that can limit the output of the flash: when covered it gives full power, when partially covered power output is reduced.
On a similar flash a 100k potentiometer is wired across two sensor terminals (each end of the thin red wire in the photo below) to control power output (_http://www.websitetoolbox.com/tool/post/rtoyz/vpost?id=2324538) but this flash has different electronics and sensor.
As you can tell I know bugger all so it may not even be possible on the photo shown in post #5
Cheers for the replies (I had problems getting on the site last night)