One thing you may need to earth the bonnet switch pin if you don't have one as iirc the oil warning won't go out till it sees a bonnet open trigger
Yeh, put in a new mk4 switch, however I think the wire needs extending, or the connector needs replacing as its not on 100% (I think). Is there a link on here to the fuel pump mod?
this is how you mod a mk4 sender to suit mk1/2/3, you see the blue wire is cut then re-soldered to the other end of the board. may want to ask around to confirm if the T4 needs it, or if its even possible as I cant say either way on that one sorry
