Inspect and clean, inspect and clean, 
Inspect and clean and retighten grounds.
Disconnect the back up lights and see if they problem stops,
Then proceed with that piece of new information.
A Bentley current flow diagram is unlikely to help.
The back up light switch is in the auto trans shifter consol. 
It likely would either be poor ground connections somewhere, possibly a
faulty unit or switch,
Though my hunch it is more a matter of re-doing the connections and grounds.
I doubt this is happening, but the wrong kind of bulb somewhere ( like two
filaments instead of one ) can cause all kinds of weirdness.
Use 'substitute and bypass' tactics - disconnect and eliminate until you
have one thing working right, then gradually add back in until you find when
things change....then focus there etc.  
I find *all kinds* of corrosion, even insects and animals damaging wires and
connections.  I can just about see from here a rear tail light assembly full
of water and the circuit board back there a nasty rusty mess.   I treat
everything with WD-40 personally.  Displaces water and prevents rust. 
Scott
www.turbovans.com 

most likely fault ? ....'owner neglect'  !! ..sorry, couldn't resist !
hope you get it !! 
"it's just a blockage or leakage of fluids or electrons." 

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
mordo
Sent: Monday, December 03, 2007 11:42 AM
To: vanagon@GERRY.VANAGON.COM
Subject: bemused by wiring

I'm no genius when it comes to wiring diagrams - I think it's somehow
related to math aversion. I have an electrical gremlin that makes me chuckle
a little that maybe someone can shed light on:

When I use the right turn signal, the reverse lights flash along with the
turn signal. This doesn't happen when I use the left turn signal. Likewise,
when I put the van in reverse, the right turn signal lights up, solid, not
flashing. This morning I noticed that when I move the auto trans selector
from D to N, I can hear the turn signal flasher relay click. Or maybe it's
not the signal relay? That seems the most likely.

Do these lights share the same circuit? If so, what and where is the most
likely fault?

--
mordo
1990 Carat