I have hooked up Vanagon radios to the key buzzer wire from ign
switch under the steering column.

I think it is the grey wire with black stripe.

Basically the radio has power whenever the key is in the ignition
cylinder, no need to turn the key, just inserting the key provides
power.

Note, most modern radios require a hot all the time connection to
keep the clock/radio settings and a separate wire for power when the
radio is operational.

-paul