CC head diagnostic only shows 12.0 volts

[Ed Kellock]

And I have 13.6 at the jump start post and the dash gauge reflects that as
well.
 
91 200q20v Avant with 248k.
Threw the alt belt two days ago.
I punched up the volt reading on the cc head and it was still over 13 volts
when I got home and shut it down.
I installed a new belt yesterday and the IC gauge is fine, but channel 11
only shows 12.0 and it doesn't change.
I googled for an hour last night and couldn't find any info.  I know I've
seen it mentioned in the past at some point.
I'm going to dive into the manuals now.
Just a quick post in case anyone's got a quick answer.
 
Thanks!
Ed