[urq] oil pressure gauge gremlin

[SpotatAshleys]

Here's a question for an Audifan with a WR engined quattro (or intimate knowledge WRs)
I want to fit a VDO oil pressure gauge (and oil temperature gauge) from a Coupe GT. Currently, the car (an '87 WR) has a two terminal oil pressure sender (terminals presumably marked WK and G - WK for autocheck and G for gauge). One wire (Blue with white stripe) is connected to one of the terminals but I can not see which terminal.
To test the gauge before trying to fit it I connected the gauge signal wire to the (currently) unused terminal on the sender. When the ignition was switched on, it resulted in the gauge needle going all the way across the scale suggesting a short to earth. I deduce from this that I had used the wrong terminal (as I say, I can not see which terninal is which with it in situ). So I disconnected the blue/white wire from the other terminal on the sender and connected the new gauge signal wire to this. Now when I switch on the ignition and start the engine the gauge works correctly. Only problem now is that the oil pressure light on the dash stays on all the time and the auto check lady keeps telling me to check the oil level.
Anyone know a) what is happening b) what should be happening c) what sender or senders the car should have and what they do, and what colour they are/ part # etc.
I do have another drilling in the block that could take a second sender if that will achieve what I want i.e. the gauge to work and the autocheck to function as it should also.
I would stress that I know for certain that there is no problem with oil pressure or oil level. This is purely an electrical issue.
As always, any information gratefully received.
Many thanks

Keith

'87 WR