I had a similar problem with Folly ('84 A'wagen)...  Here's what I did:
the 12v supply to retain settings goes to fuse 7 or 8. (dome light circuit I
think that it's 8. Most wires on the backside are red. Always 'hot')
the 12v power goes to the rear slot of where the key buzzer used to be. (you
may need to poke around a bit. Find the slot in the relay panel above the
fusebox that has 12v when the key is in the ignition and no 12v when the key
is removed. On mine it was the slot that is closest to the front of the bus
when the fuse panel is in place. Note: you'll need to remove the 2 phillips
head screws to lower the fuse panel to access the above.)

Now your radio will retain the settings and the power to the amp will be cut
when you remove the key.

Jim

----- Original Message -----
From: "Don Hanson" <dhanson@GORGE.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Tuesday, September 09, 2008 8:21 AM
Subject: Re: Stereo

> Oh yeah...Mine loses it's settings
> and returns to 'default' settings when you withdraw the power.  It also
> draws enough electricity, just sitting there off so that my aux battery
> will
> go flat in about 4 days without me turning on the stereo.