Take a look at my article about this problem.  It is pretty comprehensive:
http://www.vanagain.com/troubleshoot-the-oil-light-and-buzzer/

Ken

On Thu, Oct 1, 2015 at 3:29 PM, Aaron <a.robinson.lists@gmail.com> wrote:

> Hello all.
>
> We have a ’91 automatic that is currently giving us an oil buzzer warning
> and I think it may be a false alarm, but perhaps not.
>
> History:
> • 200,000 miles. Original engine.
> • Has occasionally given the buzzer when on hot, long trips coming off
> freewa.. Typical vanagon. Not too concerned
> • 3 weeks ago oil cooler seal failed pumping 2.5 quarts out the back over
> about a mile & leading to an oil buzzer, immediate shutoff, and a short tow
> home.
> • That was fixed and the van has driven fine since then. No oil buzzer
> • 20w50 and Mahle? filters.
>
> So, one might ask “Where there any unusual events that might trigger this
> sudden oil pressure light?”
>
> As usual…probably me. Over the weekend, I started finishing the brake work
> which means a new master cylinder and rear brakes. I swapped out the master
> cylinder, put the dash back together, and took it for a spin. Oil buzzer
> went on as soon as I started driving it up the road. I stopped it. started
> up again, and same thing. Oil light comes on once I rev past 2000 or 3000
> (can’t remember) RPM’s. Due to the fact that things were fine BEFORE I tore
> apart the dash, it might indicate that perhaps there’s gremlins in the
> electrical.
>
> I did some checking and my hope is that this is because of an electrical
> issue related to my “handiwork” on the brakes. I cleaned the contacts at
> the big plug where the oil pressure sender wire is with no change in the
> behavior. All contacts look good anyway.  I was careful with the dash bits
> and hopefully didn’t damage anything.
>
> If this is indeed electrical, are there “typical” issues that can help me
> to diagnose whether the warning is an electrical issue or actual oil
> pressure issue? Please don’t answer “get an oil pressure gauge”. I’m hoping
> for some multimeter readings etc...
>
> Meanwhile we drive the spare.
>
> Thanks!
> Aaron
>
> ’91 Carat (daily driver)
> ’87 Westy
>

-- 
Thanks,
Ken Wilford
John 3:16
www.vanagain.com