[KS6KGR]

Where does the 4 connections from the gauge connect to on a mk3 çavalier.

 

[Harvey]

I'm assuming as follows:
Grey/ green - ign dash light, ciggy light possibly.
Black - ign +'ve
Brown - earth
Blue/ yellow - oil pressure switch & not the oil pressure warning switch being blue/ green

If you can put more details of what your actually installing it'll help plus the search feature on here is very good.