Harry:
I've repurposed my oxygen sensor light to act as a check engine light.
 And i used the lower right location (just to the right of the ox2
light) to place a new led (there was no bulb there before) which acts
as an emergency brake indicator (the steering wheel blocks my view of
the stock one).

Here's a pic of the blue foil showing the repurposed ox2 bulb and the
newly inserted e brake bulb.
http://www.weidefamily.net/vanagon/Pending_Content/Engine_Conversion/06RunWiresToDashAftermarketGauges/01ECUAndEmergencyBrakeLightLED.JPG

Heres a pic of the finished product:
http://www.weidefamily.net/vanagon/Pending_Content/Engine_Conversion/06RunWiresToDashAftermarketGauges/06InstrumentClusterAndPillarGauges.JPG

Repurposing the oxy light is fairly straight forward.  You do have to
do some modification of the wires that feed the instrument panel
though.  I've got a diagram of what needs to go where here...
http://www.weidefamily.net/vanagon/Pending_Content/Engine_Conversion/20ECULight/SubaruVanagonECULightWiring.pdf
I fed my ecu light from my vanagons subuaru engine ecu.  Its important
to note that the way i've wired it works well with the suby ecu
because the feed coming from the subaru ecu for the light is a ground.
 If your ecu check engine light sends out a power feed, you'll not be
able to use my instructions.
Here's a written set of instructions that support the pdf above...
http://www.weidefamily.net/vanagon/Pending_Content/Engine_Conversion/20ECULight/UsingTheHiPressureOilWireForECUMilLedFeed.txt

As to putting a new bulb in one of the dummy spots.....
Inserting a new bulb in the lower right position is not for the weak
of heart.  I did it only because i don't know any better.  You have to
poke a hole down through the blue foil - avoiding any traces that
thankfully are easy to do in the lower right position.
Then, you tie into the exposed legs of the led with wire feeds that go
off to whatever you have that will send a power and ground feed to it.

Hope that helps a bit.
Brent

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Brent Weide
Portland, Oregon
www.weidefamily.net/vanagon/