Sam, this buzzer system is notorious for giving off false warnings.  I mean
at inital start up your oil pressure is super high (like around 65 or 75
psi).  So if there would ever be a time that the buzzer wouldn't come on it
would be inital start up.
Here is what I would do:
Unplug the wire from the sender.
Plug it on the spade connector on the side of the distributor that is not
hooked to anything.
Now run the van.

If the buzzer is still coming on then you have either a wiring problem or a
"L" board problem.  If the buzzer stops coming on then you have a sender
problem.  Since it is less than $10 I would recommend replacing the sender
and hooking everything back up.  If you still have the buzzer after this,
then take it to a local shop and have them check the oil pressure manually.
This would give you an idea of what is really going on here.

I hope this helps.

Ken Wilford
http://www.vanagain.com
John 3:16

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