Thanks boobatron3000 and nox86 and sorry for not getting back sooner. I still haven't managed to get this board to work and I suspect I might have broken it by now. I'm probably going to buy another LCD so we'll see what strange new board design I come back with.
Here's what I tried
Soldering the red wire to the small, right tab on the AMS1117 regulator ( nothing happened)
Soldering the red wire to the large, top tab on the AMS1117 regulator ( nothing happened)
Soldering the red and black wires to the 5V and ground points nox86 pointed out ( still nothing)
By now I thought I'd probably messed the board up in some way with all my dodgy soldering and accidental slips with the soldering iron. So in one last attempt to see if I could get something at all to happen I replaced the red wire with a 20V one, and after a couple of sparks the lcd started smoking. (something happened
I'm new to soldering so that might be why I couldn't get it to work, also I'm using a raspberry pi b+ with this cable "https://www.modmypi.com/audio-video-composite-cable
". Not sure if that makes a difference but I tested the cable with the pi and another tv so I know it works. Thanks again and hopefully the next LCD I get wont have to meet the same end