Well, if you have a 1.9l engine, you don't have a .9bar oil pressure
sensor. The later model clusters have a dynamic oil pressure system
circuit board that monitors the tach and starts watching the .9 bar
sensor insteadd of the .3 bar sensor at engine speeds over 2000rpm.
Until the tach wire was connected, it didn't know you were over
2000rpm. Since the .9 bar switch is an "open below .9, closed above"
type, it sees your lack of a switch as a low pressure condition.

On 5/16/05, Michael Knight <vwdormer@hotmail.com> wrote:
> So I finally got off my hump this weekend and ran a wire from the front of
> my 85 Vanny to the rear. Connectiona wer made at the - side of the coil to
> the green wire for the Tach. This entire cluster came from an 87, I replaced
> the entire unit. The tach works excellently. But the oil pressure warning
> system has changed.
> 
> Prior to the connection the oil light would flash at idle or low rpms, then
> it would stop blinking at the touch of the accelerator.
> 
> After connecting this wire the light never stops blinking and after about 30
> sec. there is a buzzer driving me crazy! It sounds like the key buzzer but
> with a different pitch.
> 
> Have any of you ever experienced this before?
> 
> Thanks,
> 
> Michael Knight
> '77 Westy Deluxe, "el Verde"
> '85 Vanagon GL, nameless
> http://photos.yahoo.com/electrictrain@sbcglobal.net
>