Okay, the 91 non-GL Syncro I bought last year, had a crappy FM only
radio. I had a Pioneer AVIC N2 to put in its place. Since I had
bought from Crutchfield they had a lovely harness adapter so that I
could keep the "stock" wiring.

So I pulled the original (don't think it was OEM, but it still used
the stock wiring ) radio. And started installing the Pioneer.

Wired up all the speakers, and hot lines, illumination and "acc" line
(hooked to the X circuit on the Vanagon.) Attached ground and tried
the unit (not yet installed in the dash.) Nothing.

Double check my wiring. All fine...Double check the adapter wiring to
factory connector....all fine...except. The factory wiring had no ACC
wire (plug, yes, but no wire.) Well that explains a lot.

So I crimped into a nearby X wire (black/red going to the front air
switch) Voila. It worked.

Of course in order to get to that wire I had to pull the levers off
and broke one. Sigh.

Then I had to route the wires to the "remote" unit of the Pioneer.
This is part of the GPS navigation system. It has to be oriented flat
(so I couldn't hide it behind the glovebox for example. So under the
front drivers seat it went. I routed the cable under the rubber mats
(had to lift up the accelerator pedal to do so.) There were 3 cables.
Extender cable for radio antenna. Main connector (multipin) between
the pioneer units, and a cable to the emergency brake switch. All
connected, all happy.

Went to reconnect the accelerator pedal and the rod at the top came
up in my hand. Sigh.

Under the car and remove the cover (so I had light and could see what
I was doing.) Then reconnect the rod, and the pedal. Easier than I
thought it was going to be.

Then I had to button it all up again.

There's a reason install places charge a couple hours for this type
of thing...