Cheers.
The 3V wire was formally part of the on/off switch. The 3V wire, is grounded by the on/off button to turn the camera on and off.
Your suggestion is completely correct, and so far as I can tell, on that basis my usage of the transistor should have the desired effect.
If I send the 'base' pin of my transistor high, the 3V wire to the collector and the ground to the emitter, I *should* be sending the 3V wire low? But this doesn't seem to be happening. I was wondering whether I have over simplified the problem, or have completely misused the transistor.
And that is the crux of my problem. Hopefully this has removed the ambiguity in what I was asking.