Installing 2 more gauges in my dash panel, voltmeter and oil pressure.  Question for anyone who did this already:
Do I remove the factory sensor and install the gauge sensor in this port (rear port above oil filter), or can I use the other port next to it (the left port above the oil filter)?  I am wondering if the left port is left for some other purpose, or if it an "auxiliary" port for installing a gauge like I am?
I included a picture.  Click on it to enlarge

i used the factory port and it works fine.

So what do you do with that factory connection?  Leave it hanging?  Does the idiot light malfunction at all with that disconnected?  I can't even figure out how to disconnect that one, that plastic cover seems stuck on pretty tight

The 'aux' port is too small to take a standard size adapter, you want an M10x1 thread for the block. I bought an adapter with the M10 thread to the block, an M10 thread for the stock oil pressure switch and a 1/8 NPT thread for the gauge. The T piece is remotely mounted with a flexible pipe to the block, I have heard of the solid T pieces cracking.
Some ECUs require the connection to the oil pressure switch.

Is the wire that is already there an actual pressure sensor?  Or does it just shut off the engine if there is no oil present?  Mine is an electrical sensor; if I could tap into that, I can try to find an electrical pressure gage instead of mechanical

Listen to the Rhinoman - especially about that flex.

I am confused, and I just spent an hour at the auto parts store and gained no progress.  That thread pitch on the OEM sensor is impossible to find.  I am confused: rhinoman, did you use an electrical or mechanical gauge?  If electrical, did you just use the OEM sensor for the idiot light?  If mechanical, did you use the front port that is plugged up?

After reading more carefully, your setup goes BLOCK -> flex line -> tee fitting -> SPLIT into -> M10x1.0 OEM idiot light sensor and SPLIT -> 1/8" new gauge sensor tubing???  That way you retain usage of the OEM idiot light, and add in the new gauge tube?
Where did you buy that adapter and flex line???

I used a mechanical gauge on mine I just unscrewed the one there and treaded the adaptor that comes with the guage in then ran the little hose in the cab and hooked the gauge up. I dont remember what i did with the wire that is there. but i dont have any lights on or anything.

No the standard idiot light sensor cannot be used with a gauge - it is a switch, either on or off, you MUST get a sensor that matches the gauge you are using if you use an electrical gauge.

I've used the Equus gauge sets (available from Walmart among other places) and they come with a metric M10x1 to 1/8 NPT adapter that screws directly into the factory port - these adapters are also sold separately by both Equus and Autogage and may be available off the rack at your local AutoZone of whatever you have in your neck of the woods.

It might also be an idea to use 1/8 copper line rather than the 1/8 nylon that is usually provided with the gauge - two reasons, one - if you kink it, that's it, two - it has a tendency to creep in the unions and may leak, I had one leak at the gauge (which was mounted above the CD deck - which has never worked since)

I see.  Yes, I bought two Equus gages at Kragen.  A voltmeter and mechanical oil pressure.  Today I found out there IS an electrical oil pressure for twice as much $$$ and requires a corresponding sensor to work with it.  Rhinoman, do you have a picture of that tee/adapter you can post up?  I wasn't able to use the adapters in the Equus tubing kit, they are not the same M10x1.0...look close but a lot coarser and slightly larger, I believe 1/4" NPT.
I think I actually have some of that copper in my tubing stash in the garage...

Mine is an electrical gauge. The adapter is this one, although I bought it seperately from a local motor factors

http://cgi.ebay.co.uk/SUBARU-OIL-PRESSURE-OIL-TEMP-GAUGE-FITTING-FULL-KIT_W0QQitemZ350214595394QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item518a6aa342&_trksid=p3286.c0.m14&_trkparms=65%3A12%7C66%3A2%7C39%3A1%7C72%3A1689%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50

I'll be trying to track down adapters.  Will the other plug in the block give the same reading as if i used the original one?  Has anyone done this?

The other problem I was having is that at the auto parts store, half of the items marked "M10x1.0" matched my OEM sensor's threads, and the other half didn't.  It was impossible to find.  There's an Autozone and NAPA I have yet to check though

From memory, the other hole goes into the same galley so will give the same reading but its something like an M6 or M8 thread.

I've gotta work today, my dad is going to the local auto specialty place (deals with VW specialty) and finding the metric thread pitch for a flex line, tee, and 1/8 npt for the gage