Ron-
     
     Here's an idea for another FAQ.   I've taken the basic information 
     that Ken Lewis (kdlewis@juno.com)  posted on Aug 18, and added a 
     detailed explanation based on my experience (and early-June post) 
     troubleshooting MY system.
     
     ******************************************************************
     
     How works the "Dynamic Oil Pressure Sensing" System
     by Blaine Bachman (blaineoftrains@earthling.net) 
     and Ken Lewis (kdlewis@juno.com)
     
     PREFACE
     This is not intended to be a complete guide to troubleshooting the 
     Dynamic Oil Pressure Sensing System.  Rather, it is intended to 
     familiarize the reader with the essential pieces of, and logical 
     operation of the system.  The idea is that once you understand what's 
     happening (or supposed to happen), you can get out the Vanagon Bentley 
     Service Manual and follow the troubleshooting steps which span several 
     pages.
     
     BASICALLY...
     The Wasserboxer engine is similar to most other VW watercooled engines 
     in that it has two oil pressure switches electrically connected to a 
     circuit board (behind the tach or clock - often referred to as the "L" 
     board) which controls the idiot light on the dash.
     
     The low pressure switch is located on the left side of the Wasserboxer 
     engine case, between and below cylinder 3 and 4 and hidden by some 
     engine tin.  This switch operates similarly to the single switch many 
     of us are used to from our air-cooled days: when the pressure is low 
     or zero, the circuit is "made" (closed).  When this happens in the old 
     Beetle, the ground circuit is made to the idiot light, causing it to 
     light if the ignition is on.  When the pressure rises above the preset 
     level, the switch opens, extinguishing the light.
     
     On the Wasserboxer, this switch, when functioning properly, opens 
     between 2.2 and 6.5 psi.  Rather than go directly to an idiot light, 
     this switch connects to the "L" board.
     
     The high pressure switch looks pretty much like the low pressure one 
     (except for having a different color of plastic end) and is located at 
     the rear of the engine, above and slightly to the left of the oil 
     pump.  It's pretty hard to see, and almost impossible to get at, but 
     it can be replaced with a little work.  This switch works just the 
     opposite of the typical oil pressure switch in that it is normally 
     open (does not make contact) until the pressure rises above a certain 
     level.  On the Wasserboxer, this switch must CLOSE between 10.9 and 
     14.8 psi.  It also connects to the "L" board.
     
     The "L" board takes the input status of the two sensors, plus the 
     "count" from the tach input and causes the LED to flash and the buzzer 
     to sound based on an internal "truth table".  The various combinations 
     are pretty well illustrated in the Bentley Manual, but here's a brief 
     synopsis:
     
     1. When the key is on but the engine not running, the LED should 
     flash.  If it does not, the circuit to the low pressure switch 
     (including the switch itself) should be checked.  Problems with the 
     LED, "L" board, or voltage stabilizer are also a possibility.
     
     2. Shortly after the engine is started, the LED should stop flashing 
     and turn off.  If the pressure at the low pressure switch drops below 
     the switch's limit (closing the circuit) at any time while the engine 
     is running below ~ 2000 RPM, the LED should flash.
     
     3. Whenever the RPMs pass above ~2000, the high pressure switch is the 
     focus of the system.  When the "L" board senses the revs above ~2000 
     and the high pressure switch shut off, it believes that the oil 
     pressure has dropped below the limit needed to guarantee safe 
     operation.  To get your attention, it flashes the LED and sounds the 
     buzzer.
     
     If you're having problems with condition 1 or 2 above, probably the 
     easiest thing to do is to change the oil and filter (reams have been 
     written on problems with U.S.  made filters on the Wasserboxer - go 
     with the Mann, Mahle, or VW filter) and the switch.  While you're at 
     it, do a simple test on the wire by grounding it to the engine case 
     and checking to see that the LED flashes while the key is turned on, 
     and that it stops flashing when the wire is ungrounded.
     
     Problems with condition 3 are a bit trickier, and can be compounded by 
     problems with conditions 1 and/or 2.  The first step, is to probably 
     do the oil/filter change recommended above.  The problem may go away, 
     but maybe it won't.  Either way, since the high pressure system is so 
     critical, you should complete the remainder of the troubleshooting 
     process found in the Bentley Manual.  At any rate, if your LED/buzzer 
     come on immediately and consistently once the engine revs over ~2000 
     RPM, you either have a serious oil pressure problem, a faulty high 
     pressure switch, a bad connection, or a bad "L" board.  If it only 
     comes on when the engine is hot, you MAY have an overheating problem, 
     either alone, or in combination with others.
     
     PRESSURE SWITCH NOTES
     
     In theory at least, all points of a pressurized system should have the 
     same pressure.  This is generally true in the Wasserboxer, however it 
     doesn't take a total failure to render a pressure switch faulty.  
     Weakening of the spring loaded contacts and clogging can also occur.  
     Both situations are bad for either pressure switch and can cause 
     erroneous readings at the "L" board and subsequent "false" alarms.
     
     As already noted, replacing the low pressure switch is a "piece of 
     cake".  The high pressure switch is another story.  You pretty much 
     have to have a 24mm socket.  (Sears' deep socket is too long to fit in 
     the cramped space, and the normal one is too short to fit on the 
     switch when the ratchet is inserted - a "half long" socket would be 
     perfect, but we'll show how you can use the short one).  Further 
     "icing on the cake" is provided by Bentley's rather cryptic comment to 
     slide some piece of tin aside to get at the switch - this didn't bear 
     any relation to reality on Blaine's '91, but may with earlier models.
     
     Best way to start is to first remove all the V-belts.  Disconnect the 
     wire from the switch.  Put the shallow socket on the switch.  Put the 
     3/8" to  1/2" adaptor on the 3/8" drive ratchet; Grab a hold of 
     "killer" (the  big, long Craftsman screwdriver that can double as a 
     pry bar) and use it to push the socket as far out on the switch as 
     possible but still allow the socket to catch the switch.  Stick the 
     ratchet/adaptor on the drive end (again, just part way on, because the 
     terminal is sticking into the drive hole); turn.
     
     With any luck it won't fight you on the way out.  The insert may come 
     out with the switch, but that's a quick fix; just remove it carefully 
     and thread it on the new switch.  Get the whole thing rethreaded and 
     tight.  Wire on and belts tight and you're done!