Entering security code - NF / EF Fairmont?

[spope]

Does anyone know how to enter the security code on the standard headunit out of an NF Fairlane (and EF Fairmont, I believe) - the single din headunit with stacker controls.
I wired up the headunit, 90% sure all connections are good, except i don't have the plug for the rear speakers, gonna get that tomorrow.
Anyway, electric antenna goes up, stacker has power, i can eject the cartridge and all that.
The display is just flashing "Err" I am under the impression I should just have to leave the key in the ignition for half an hour or so and the unit should reset and allow me to enter the code.
But I don't know how to enter the code! The code I have here has zeros in it, and you can't enter zero's with the radio preset buttons, can you?
Or is it likely that I have an incorrect code?
Any info would be greatly appreciated.
Also, if anyone has any diagnostic info, as to what other things may cause it to flash "Err," it would be most welcome.

[JC]

is it a 4 digit code? From memory, you use the buttons 1 to 4 to enter the code and each press cycles through the numbers from 1 to 0, or maybe from 0 to 9.

Or not.

[NZ]

it should only have the numbers 1 - 6. turn on, it will say 'codE' press the buttons. if you get it wrong you get another go
and another
afte rthat you hafta wait
and each time you balls it up you hafta wait longer