'97 C4 - radio won't turn off with ignition off - it pops back

[khnitz]

Here's the problem: with an aftermarket Blaupunkt radio, when the car is turned off, there is a momentary "blip" where the radio starts to turn off ("Go..." is visible of the Goodbye message for a moment), but then the radio stays fully powered on.  I'm trying to help my friend sort out what may be wrong with his wiring that this would happen.

 

The background: I'm helping a friend sort out the audio system on his 911 - it's a 1997 C4 that had the Hi-Fi sound option.  When he purchased the car, there was an aftermarket deck in the dash and the amplifier connector had been by-passed (a total hack-job on the wiring).  I repaired all the wiring back to its factory original configuration so that we could re-install the correct Nokia amplifier.  At that time, he just wanted speakers on the rear deck.  So those were left connceted, and a pre-amp unit (a VC1 from V8A - V8Audio) was installed out-of-sight behind the dash for a minimalist look.  The factory radio mounting location was used to relocate the switches from the center console. too.

 

Smash-cut to now, and with some changes in taste, the rear speakers have been removed and speakers are now in the front doors again.  Also, a modern Blaupunkt stereo was installed.  The "won't turn off" issue is the last thing to sort out this upgrade.  I have verified that there is constant power (battery) and Ground at the proper pins of the radio, but what should be the switched ignition signal on pin 7 (in the wiring diagram, this line is labeled as "R" ?) is at a voltage just below battery (Battery=12.8VDC, "Ignition"=12.4VDC).  It also measures a momentarily blip at key-off, but then recovers back to ~12VDC almost immediately.

 

Any thoughts on what may be happening are appreciated!  What else does the "R" signal line connect to?  Could it be the result of a bad ignition switch or power distribution relay?  In searching for an answer, those seem to come up as possibilities, but not with the symptoms he's seeing.