I plugged the HU in using the ISO connector and it came on fine.
Turned it off and it wouldn't turn back on. Fiddled about checking wires and connections/unattaching connectors etc. and eventually it came back on.
It seems that whenever there is a cut in the power (eg. I turn it off/I turn the key to start the car (position III)/I turn the key to the off position), it won't turn back on unless you disconnect the iso connector from the back of the headunit AND also disconnect the ISO connector from the other black plug with all the coloured wires sticking out of it.
When you plug them both back in, it comes back on, but you have to repeat the process every time it goes off

Do I just need a new ISO plug or is there something else the matter?
Cheers