Ok so this morning I reduced the voltage to 11.8v and set it to 6 hours. The green LED was on so I left it and 7 hours later the cameras were still on. I decided to use my multimeter to troubleshoot. First I disconnected the power magic pro from the white connector that goes in the back and I measured the voltage on the earth pin and yellow perm 12v pin which showed 12v, then the switched 12v (with ignition off) and it was 0v. I switched the ignition on and measured the switched pin and got 12v so the power input into to PMP is correct. I then turned the ignition off and connected the PMP again. With the PMP off I measured the voltage inside the female cigarette socket that comes with the PMP and it was 12v, I turned the PMP on and it was still 12v (the green LED never turned on). I switched the ignition on and these measurements dropped to 11.8v. So it is now clear that the power magic pro is faulty as even when it is off it is providing a 12v feed to the cameras. I havfe contacted the supplier to arrange a refund, all this time wasted and it was a faulty device that caused it!