Each of the sections below represents a wire that needs to be run from the engine bay up to the dashboard.  They should all be run in a conduit or channel which will provide protection from outside damage and heat.
These wires can be run at any time before, during, or after the conversion is complete but are required to have an ECU Light in the dash, aftermarket oil pressure, aftermarket water temp, and operable tachometer (see note in Tachometer section below). Suggested additional wires are a 12v positive and ground wire.  That way you won't have to depend on any splices under the dash to run your gauges or ecu light.
Do yourself a favor and tag the ends of the wires to make the job easier.


All of these additional wires should originate right near the black box in the vw engine bay so that they can be extended to plugs which are located inside the black box, out of the weather.

MIL (CHECKENGINEGROUND) WIRE
	FROM:
		ECU F47.19 (D19)  MIL  
		The Line 19 position in the ECU D Plug up to the dash board and to the ground leg of a bulb.
	TO:
		Wherever you intend to place your Check Engine Light.
		This would typically be in your dashboard to the instrument cluster.
		The other leg of the bulb will be 12v+ Ignition On.

AFTERMARKET OIL PRESSURE SENSOR WIRE
	FROM:
		Position 1 of New Plug to be installed near engine gray plugs
		This will run through the intake manifold wiring harness and connect to the aftermarket oil pressure sending unit which is located in one of the two available oil ports in the top of the engine block.
	TO:
		Newly installed aftermarket oil pressure gauge at or around the dash cluster area.
		
AFTERMARKET WATER TEMP SENSOR WIRE
	FROM:
		Position 2 of New Plug to be installed near engine gray plugs
		This will run through the intake manifold wiring harness and connect to the aftermarket water temperature sending unit which is located in a newly drilled/tapped hole on the coolant manifold on top of the engine block.
	TO:
		Newly installed aftermarket water temperature gauge at or around the dash cluster area.

TACHOMETER WIRE
Note:  If you are using a modified/calibrated tachometer, you can use the stock vanagon tach wiring and require no additional tach wire.

	FROM:
		>>>>>>>>>>>>>>
		
	TO:
		VW Tachometer
		
12V+ Ignition On
	FROM:
		Yellow lines in wiring harness
	TO:
		This will be 12v+ Ignition On line and can be used to power the ecu light as well as the gauge power needs.


EXTRA WIRE
	FROM:  This could later be used for a VSS or other line as needed.  Cheap Insurance.


Here's a great tip I picked up through Seth Hatfield of H&R Motors.  Just go down to the hardware store and purchase a 50 foot extension cord.  That'll give you enough wire for 6 separate 25 foot runs.  More than enough to run from the engine bay up to the cockpit to push aftermarket gauges, a check engine light, and a few other things with wires to spare.  And, they come in their own shielding for around 6 bucks or less.

As to the route for the wiring run, here's the direction I took.  I started my wire run from the black junction box.  Any wires that needed to feed to the dash from the ecu, I ran from my ecu located under the rear bench, back to the black junction box inside of my wiring harness.  This part required a bit of planning beforehand and saved work later.

Starting at the black junction box in the drivers side firewall area of the vanagon engine bay, I ran back, parallel to, and strapping to, the driver side frame rail.  I took this up all the way to where the rail encountered the rear part of the 2wd gas tank.  There I cut over to the passenger rail, strapping in to whatever was available along the way.  This positioned me to run my wires alongside the two radiator 1 1/2" lines toward the front of the van through the tunnel space atop the 2wd fuel tank.  Once out of that tunnel area I basically followed the radiator lines forward until I jumped off of them and started heading vertical to the area in front of the radiator, behind the front upper grill.  There's a tray of sorts at the bottom of the top grill opening which accomodates the headlight wiring.  I ran just alongside of the headlight wiring, in front of the radiator, across to the area behind the driver side headlight.  There I headed vertical up to where you'll notice a couple of grommets allowing wiring access to the area behind the dash.  There was enough room in the left most grommet for my six new wires.  From inside the van, make sure you extend the wires long enought to make it easy to tie into them from your working position with access through the gauge cluster opening (with gauge cluster removed).



Byron:  Thanks for the feedback on my site.  If you ever think of additional content that might be useful out there, give a holler.
ECU Light At Dash
I strongly believe that having the light up in the dash is the way to go.  It's useful in that you don't have to open the engine compartment or the bench seat (depending on the ecu location) to read your codes.  If done properly it looks like it belongs there because vw was kind enough to leave some led spots open just for us to use!!! 
The downside is the constantly blinking codes which may or may not be present, even with a perfect conversion.  As you may know, the earlier 90-94 engines, even when converted using KEP's smog legal instructions, leave you with codes 51, 52, adn 33.  The later engines typically leave codes as well but I am not quite as familiar with what actual numbers they are.  The fact that some codes are expected is the reason that I installed a small toggle switch under my instrument cover that allows me to shut down the light when I'm not reading codes and removes a distraction.  If you got crafty you could install the switch in a location under the dash where you'd not need to do anything but reach down and flick it on or off to make the change. 
I've done 4 conversions now and continue to install the light in the dash.
 
The subaru ecu provides the ground leg of the wiring to the led.  You have to decide where to get the 12 volt (ignition on) feed to the led but it could even be from up under the dash.  I decided to run all of the wires for my ecu, water temp, and oil pressure system all at once and tie them all in at the black plastic junction box in the engine compartment.  This makes it easy for me to remove the engine by disconnecting the wires back in the bay.  I used a newly purchased 25' outdoor extension cord (about $10 from home depot) for the wiring run from the engine bay, under the van, behind the front grill, and up into the grommet behind the driver side headlight where they enter the cab of the van.  Because the extension cord has 3 wires, I am able to get a total of 6 wires when doubling the cord back on itself for the run.  This is enough to accomodate the following: 
Oil Pressure + (from block oil journal sensor to aftermarket gauge at dash)
Oil Pressure - (from junction box ground connection to aftermarket gauge at dash)
Water Temp + (from coolant manifold sensor to aftermarket gauge at dash)
Water Temp - (from junction box ground connection to aftermarket gauge at dash)
ECU Light + (from junction box 12v ignition on to dash led)
ECU Light - (from ecu to dash led)
 
I picked up a 12 v power source to light up the gauges by splicing into the cigarette lighter bulb.  This allows the gauge lights to be controlled by the dash rheostat.
 
Here is a link to some additional pics and notes on the topic.
Go to my website....
http://www.weidefamily.net/vanagon/
See the EngineI Section > Click on the menu item below for 
Subaru Engine Conversion Resources Menu - October 2006
From there, go to the 06RunWiresToDashAftermarketGauges link.