You are onto something. I never mentioned it for this symptom as a bad ground on the engine can cause so many other problems. The alternator path includes the engine case and the grounding at the left head and transmission. If there is a higher resistance there than there should be you will get a voltage drop that will appear between the engine case and the chassis. This can interfere with the oil pressure warning system as that signal has to go to 0 to keep the light and buzzer off. 

With the engine running and a lot of electrical consumers on measure the voltage between the engine case and the chassis. If you see a voltage approaching 1/2 volt or more that is a problem. After repairing the original grounds a separate on from the alternator to the chassis is a good idea. I have also found that excessive resistance in the power circuit from the ignition switch back can also cause havoc. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Herb Harmison
Sent: Monday, November 9, 2015 11:35 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Oil pressure light and buzzer

Dennis,

My '91 Vanagon had a buzzer/oil light problem for the past three summers when driven on the interstate and even in town.

I did everything mentioned on the mailing list, I think. Then figured I would try changing the ground strap from the engine to the frame. I worked.
800 miles with a trailer in August in Iowa and Minnesota and not a peep from the oil signaling system and nothing since.

Good luck.

Herb

On Sun, Nov 8, 2015 at 9:29 PM, Dennis Haynes <d23haynes57@hotmail.com>
wrote:

> Be sure it is the correct one and a good one at that. BTDT enough with 
> bad switches I get them from the dealer. Pricey but the aftermarket 
> stuff is just not consistent and the dealer one have had the set 
> points changed a bit to reduce the falsies.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On 
> Behalf Of John Rodgers
> Sent: Sunday, November 8, 2015 3:14 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Oil pressure light and buzzer
>
> Thanks, guys. I think I have a bad switch, judging from the way the 
> system is behaving. Tomorrow I will put in a new one Ihave on hand.
>
> John
> On Nov 7, 2015 21:37, "John Rodgers" <jrodgers113@gmail.com> wrote:
>
> > I'm trying to get it in my head how the dynamic oil pressure warning 
> > system is supposed to work. I have an intermittent fault where the 
> > oil warning light and buzzer come on at odd times and I need to 
> > understand this monster. Comes on at different speeds/rpm. Oil level 
> > is fine. But it's a bit scarey!
> >
> > Anybody?
> >
> > John
> >
>

--
Herb Harmison
2692 Meadow Glen Rd
Ames, IA  50014
herbharm@gmail.com
515-292-7059 Phone/Fax
515-450-7637 Cell
Skype: "herbharm"