http://www.gnttype.org/techarea/body.../oilgauge.html
http://www.ajlc.waterloo.on.ca/cgi-b...2f199604%2f132
Follow your turbo's oil feed line down. There is a "T" down near the oil pump. The idiot light sensor is down there. Having the lower radiator hose off will aid access, as I recall.
If you want to retain the light as well as the gauge, you will need a "street tee". Put it in place of the sensor, then put the sensor and your gauge sensor in the street tee.