This sounds like a ground wire problem. If you look at the Bentley
diagrams you will see that the dash items mostly ground to Ground 81.
Ground 81 is just a hidden point in the dash wiring harness where 6
brown wires are crimped together with one of them leading off to the
Ground 30 chassis ground point behind the fuse panel. That wire or its
end are likely your problem.

While they have separate POWER connections, VW connected almost
everything in the dash  to a single ground wire and then ran it to the
vehicle ground point behind the fuse panel. When the common ground wire
has problems, it affects multiple seemingly unrelated devices. That
ground point suffers from corrosion where the wire plugs onto the male
spade connector ring. Figuring out which one of the brown wires
connected at the connector ring may take some doing. A simpler approach
may be to add a new ground wire to the brown wire coming out the back of
the cig lighter socket. VW should not have combined so many things onto
a single ground wire to begin with. Having the cig lighter and dash
heater fan on the same ground wire as the dash warning lights and gauges
was unwise.

Mark

Bob Turnbull wrote:

> I have a mobile phone handsfree which plugs into the lighter socket, to
> provide phone charging and speakerphone.
> This works fine in my other vehicles, but in my vanagon this causes the
> flasher relay to buzz (not the normal click) and the oil pressure light
> to flicker when the ignition is on.
> The socket is always live, and the handsfree works fine, causing no
> problem with the ignition off, but not with the ignition on or the motor
> running.
> The relay and oil pressure light are fine without the handsfree plugged
> in -- what is happening to cause this?
>
> Bob Turnbull
>
> 91 Syncro
>
>