oil pressure last wire.

hi all. never like asking for help but I'm stuck with this. background is abf in to my s1 78 gls. been through all the wiring in the car now , all working fine bar the oil pressure warning lamp. the car uses a duel circuit hand brake/ oil pressure warning lamp system. 99.9% sure the wiring is correct as the oil lamp aluminates when the oil pressure wire ( blue/black) is earthed out . question is witch one of the two pressure switches is meant to be used for s1 loom off the abf . second question is dose any one have the data to test these switches. i have tried both switches at ignition on and running the engine till fan cut in  but can not get any signal off either .  thinking that the switches control the earth. might b missing the obvious . but i do need this system as i have no warning and don't want to kill the engine . thanks ric

i dont know the ABF engine at all , but am assuming you cant try the original senders/switches in ?

Old unit has gone. What your saying makes sence , ill look in to the original senda should fit fingers crossed.

i'm not at all well versed on all the technical specs , but a tryer lol