This thread has details on the modification you're after. See the post by
syncrodoka.

http://www.thesamba.com/vw/forum/viewtopic.php?t=252765&highlight=door+lock

On Wed, May 9, 2012 at 7:56 PM, Craig Cowan <phishman068@gmail.com> wrote:

> You need to be able to lock them so you can say to your passenger " lock
> that door".
>
> I'm ready to strip it down and figure it out if no one knows why.
>
> -craig
>
> On May 9, 2012, at 10:22 PM, Dennis Haynes <d23haynes57@hotmail.com>
> wrote:
>
> > Come to think of it both my 87 vans need the doors to be closed for the
> > doors to lock. The Camper does not have power locks.  I'll have to check
> the
> > '88 Fox.
> >
> > Dennis
> >
> > -----Original Message-----
> > From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
> Of
> > craig cowan
> > Sent: Wednesday, May 09, 2012 4:53 PM
> > To: vanagon@GERRY.VANAGON.COM
> > Subject: Door locks only work when doors are closed?
> >
> > On my '87 syncro, which does not have power locks, I can only seem to
> lock
> > the doors when they are closed. A key will only lock the door if it's
> > closed, and the locking "button" can only be depressed with the door
> closed.
> > This is proving to be extremely annoying and is not the case on my other
> two
> > busses.
> > This isn't normal right?
> > How do I fix it?
> >
> > The doors lock and unlock fine and with little effort while closed
> though...
> >
> > -Craig
> > '87 SUNROOF SYNCRO WESTY ZETEC
> > '90 GL "NEW BUS"
> > '85 Residence
> >
>