I've used the Grey/black wire from the key switch for radio ACC power.

It's +12V whenever you INSERT A KEY into the ignition, no need to turn the key.

when you remove your keys, radio goes off. This way you won't
accidentally leave the radio on and drain your battery.

>
>Alternatively, you could "create" an ACC connection for the radio. To do
>this you will need a volt-ohm meter (multi-meter). Pull that plastic
>cover off the underside of the steering column (assuming yours isn't
>already broken like so many of ours). Test for voltage from some of the
>wires under there. You want to find a wire that reads about 12v when the
>ignition is turned on, but has 0v when the ignition is off. When you
>find that wire, you can tap into it and and connect it to the ACC wire
>for the radio, instead of connecting the power wires together. With this
>setup, the radio will turn off when you turn off the van (like VW should
>have done in the first place!).