Location of 1.9 DG oil pressure switches

[PaulFDennis]

I’ve been working on the dash instrumentation on my 1.9 DG engined T25 (1990/91) and found the oil pressure warning LED was removed. On replacing the oil pressure warning light flashes but there is no oil buzzer sound at >2000 rpm. On further investigating I find that both the low pressure switch wire (blue/black) and high pressure switch wire (yellow) have been grounded. This explains the observations I see on the dash. I can locate the low pressure switch between cylinders 3 and 4 and will rewire this correctly. However, I can’t find the high pressure switch! I understand it is at the back of the engine below the oil pump but am struggling to find this. The Haynes manual suggests below the oil pump, others have suggested it is close to the water pump. I’d be grateful for any guidance here.

[PaulFDennis]

I should add the reason I can’t locate the 0.9 bar switch is because there is no lead to the switch. The yellow signal wire has been directly shorted to the engine block! The previous owner had a replacement/reconditioned engine fitted and it looks as though they forgot to connect up the high pressure switch and to save time simply decided to bypass it with a direct connection to ground. I’ve no idea why they did the same for the low pressure switch which does have it’s signal wire!

[Mocki]

Sounds like they fitted a early DG , which didnt have the second oil pressure sender , which would be located between the water pump pulley and the top of the oil filter housing

[PaulFDennis]

That’s very helpful Steve and explains the grounding of the yellow (high pressure switch) signal cable. Tomorrow, I’ll redo the connections for the low pressure switch.

[PaulFDennis]

This morning I rewired the oil pressure switch - new wires, new two way connector in the engine bay and all is working as it should. Feel reassured that I now have a working oil pressure warning in the cab rather than having the LED disconnected!

That’s two odd things I’ve found whilst working on the dash. The first was the isolation of the low level coolant circuit by packing the connector with blu-tack to isolate from the flexi PCB. The problem was a dirty and corroded connector at the level sensor. The second was removal of the oil pressure warning LED. The problem this time was a poorly wired circuit in the engine bay. The pressure switch had been bypassed with a direct connection to ground. The sum cost of both fixes was the purchase of a new two way connector for the engine bay. I had the wire, crimp connectors and crimping tool already.

I’ve only had the T25 for a month and thanks to the forum I’ve straightened and refurbished the gear lever and associated parts, sorted the autochoke on the Pierburg carb, and sorted the coolant level and oil pressure switch circuits.

Thank you to everyone for your help. Now ready for some adventures.