No wonder you're confused.  I would be too if this were my first conversion and I was reading all the stuff on the site about gauges and wiring and witchcraft.



Here, hopefully, is the straightforward lowdown.  I'll place my answers inline with your questions below......

 
QUESTION:
I am a little confused by all of the info out on the SubVan site about the oil pressure sending unit/gauge.  I see that most have a two post on the unit, so where do the wires connect? Don’t you only need one wire to connect to the gauge? 


ANSWER:
All gauges that I have seen have 5 positions on the back of them which require connections.  

	Sensor (sender) Signal
	12 volt lighting (+)
	12 volt lighting (-)
	Ground (-)
	Ignition 12 volt (+)

All sending units that I have dealt with have one connection.
	Sensor Signal
	Note:  Most sending units use their threaded connection to the engine block to provide a ground.

So, all that you typically run from the sender to the gauge is one wire.

As to the other connections on the gauge, you can/should get those from the dash area of the vehicle.  
	12 volt lighting (+)
		12 volt lighting positive should be connected to your vehicles dash lighting circuit so that it is influenced by the lighting dimmer switch (if you have one).  
	12 volt lighting (-)
		12 volt lighting ground should do just that, run to a good established ground connection.  
	Ground (-)
		You may as well splice your second gauge ground connection to this wire and connect them both to the good established ground.
	Ignition 12 volt (+)
		And finally, connect the ignition on 12 volt feed to a circuit in your fusebox that is only on when the ignition is on.  Yes, you could run this wire up through from the engine compartment if you are so inclined.  I cheated and picked up a wire feeding my radio.



QUESTION:
  Is this the gauge you used in your van?  
  
ANSWER:
	  Very close, I've ended up using a pair of AutoMeter phantom gauges because they are very easy for me to read and they will match my dash gauges after I apply the homemade gauge overlays.  I favor the white background as it's easier for my tired eyes.
	  One thing to know about gauges.  Although there are certainly exceptions, you're best off to get the sending unit that the manufacturer recommends for the gauge you purchase.  I don't know much about electronics  but I do know that we're just talking about a resistor that returns electrical signal back to the gauge varying by the amount of pressure or temperature it is seeing.  If you get the sender from the same manufacturer, you're sure to get a calibrated, correct signal and reading instead of sitting there having your temp gauge tell you everythings peachy while the engine is glowing white hot.
  
QUESTION:
  Are you connecting one wire to the ECU and one wire from the other sender to the ECU so the van has two sender units to compare and then one wire to the gauge?  I am taking my van in this weekend for it’s transformation but I want to make sure I can put in an aftermarket gauge for both oil pressure and water temp.

ANSWER:
	  For clarity sake, keep aftermarket gauges separate from the stock gauges.  If we're talking subaru converted vanagons here, there are actually a need for two temperature sending unit feeds into the subaru wiring harness and on to the ecu.  The ecu related temp feed is a little brown (two terminal) sending unit which screws into the coolant manifold atop the engine.  The wires from this sending unit feed into the small wiring harness which resides on the underside of the intake manifold, eventually runs through one of the two large gray plugs, through the main wiring harness, and into the subaru ecu.
	  The second stock subaru sending unit, also located on the coolant manifold (in fact, it's only an inch away from the one ecu temp sender) is typically removed to be replaced with a vw vanagon temp sending unit from an 85 or earlier (check the year to be sure) threaded temp sender.  Or, you can check the posts for info on changing the signal of the stock subaru unit to feed the vw vanagon temp gauge.  This second sender's only job is to feed the vanagon's dash mounted temperature gauge.
	  Similarly, the stock subaru oil pressure sender, located in the top of the subaru block just under and behind the alternator, can be used to supply a feed to the vanagon dash oil light.  It also runs through the intake manifold harness, through the gray plugs, through the main wiring harness, and reemerges from the harness where it can be connected to the stock vanagon wire which feeds the gauge.  This wire is located in the small black junction box in the left back side of the engine bay.  KEP and SmallCar instructions clearly spell out how and where to splice this one.
	  
	  Now, the aftermarket gauges come into the picture.  
	  First, the oil pressure gauge.
	  This has a lot to do with personal preference but I'll tell you how I did it.
	  The stock subaru oil pressure sending unit screws in through a bushing into the block.  I relocate that sender to a similar threaded port back on the right left section of the engine top.  I've got pics on my website to help you spot the new location.  The reason I move the stock sender is so that I can have more room to install the larger aftermarket oil pressure sender.  I take the plug that I removed from the second threaded port and drill it and tap it to recieve the 1/4"NTP threads of the aftermarket sender.  I then install two 45 degree 1/4"NPT street ells (male threads on one side, female threads on the other), and screw my sending unit in.  The ells allow me to tilt the sender into a position that'll fit in the tight space given.
	  The aftermarket water temp sender can be screwed into the subaru coolant manifold.  The stock coolant manifold has a spot available that can be drilled and tapped to accept 1/4"NPT threads where you can easily screw in the sender.  Or, you could choose to tap into the water lines )(outgoing) anywhere close to the engine.  Just know that the closer to the coolant manifold you get, the more accurate the temp reading will be.

SPECIAL NOTE:
	
	When building your wiring harness, it's a great idea to run a couple of extra wires from the area around the black plastic junction box (engine bay left rear) to a new plug that you'll install which'll live right beside the 2 large gray engine plugs, into the intake manifold wiring harness, and will finally emerge above the engine block with enough slack to reach to the location of your new aftermarket gauge sending units for both water and oil.  This will save you from having to run the wires later and will tuck them neatly into your harness where they are protected and give the appearance that you actually know what you're doing.
	As to running the wires up into the dash....You just have to run them under the car and up into the cabin through a grommet.  I have taken to the practice of running down to the hardware store, purchasing an outdoor 50' extension cord, cutting it in half, and ziptying it alongside the various tubes and hoses under my van between my engine bay and up into the area behind the dash.  This gives me 6 well shielded wires that can be used for the gauges, my engine code light, my tachometer feed, and still have a few spare wires.  I got the idea of using an extension cord from Seth Hatfield of H&R Motors down in SoCal and only wish I'd thought it up first.