UKPassats

ive just put a sony head unit in my 99 golf and it wont save station settings when i remove ignition key, ive had yellow wire from unit to yellow on to yellow wire in plug at same time i had red to red and its the same, if i disconnect red from plug and connect both red and yellow from unit to yellow from plug its the same, if i connect both yellow and red from unit to red from plug nothing happens, ive tested voltage and yellow from plug is 12v when ignition on but i cant get 12v when ignition off, yellow and green wire into plug will give me 0.7v when ignition off but wire from head unit do not fit into it at plug.
am i missing something here as ive never had a problem before when fitting sony head units.
the old radio that came out was on power even with key out but ive tried to refit and now no power.