Hi - having this issue at the moment.
Unplugged the 3 factory 3 din gauges, and the oil light in the dash stays on - upon further investigation, that light shows both warnings for oil press AND oil temp. So, it would appear that when the ECU sees 0V across the oil temp gauge, it throws on the oil light.
So, my thinking is, seeing that I've replaced the 3 gauges with Defi 52mm oil temp, press and water temp gauges with warning, all I need to do is to unplug the lead going to the oil light...
Looking at the (horrible) dash wiring diagram, it seems that if I pull wire 34 going into the dash, this will kill the oil light.
I don't have the car at the moment (will be a few weeks at the shop) so will try it when I get the car back.
Note, justinfox replaced his with the Defi din gauges, and didn't have a problem. Maybe these gauges plug into the factory loom, so no issues?? I can't remember who it was who installed them for him, but maybe a quick call to whoever did it would help too
Hope that helps