I just did this, oh, three days ago. No issues yet. : )
I realize that isn't particularly helpful, but fwiw the power wire for my
stereo appeared to be smaller than the key buzzer wire. You could compare
the spec draw for the stereo to the rating for the circuit.
If I leave the stereo on when I remove the key, it comes on again right when
I stick the key in, which I did not expect. It doesn't cut out when I'm
cranking the starter, either. I hope my wife doesn't grind the starter while
the engine is running.
Kind of a nifty mod all in all.

Cya,
Robert

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Jeffrey Vickers
Sent: Monday, June 15, 2009 10:17 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Key in ignition to power radio

I found the wire that powers up when the key is stuck in the ignition
(but not turned) and I'm planning on using it to turn on my radio. It
looks like a fairly small wiring carrying a small load - is there any
reason to use a relay here? What have other volks done?

Thanks,
Jeff