4000 oil pressure

[The Swanndri Guy]

While using my Ford 4000 today, the oil pressure warning light came on. I've replaced the oil warning light sender unit (81873524), which made no difference, but then I noticed that the oil warning light was still on even when I disconnected it from the sender unit with the engine running, so I suspect a wiring fault.Problem is the fault is intermittant, and when it does happens the oil warning light "fades" on and off more like the charge light at idle speed if it comes on,as if there is a voltage problem.If the wiring is OK, could the voltage regulator be on its way out?In order to eliminate oil pressure as the cause of the problem,what should the oil pressure be at idle and what should the maximum oil pressure be? And where is the best place to hook up a oil pressure guage? Will be demoted to using the 3000 until I sort out this problem TSG

[Brian]

Oil pressure should be around 60-70 psi at 1000 rpm when new so allow a little lee way here. Anything around 40 to 50 psi should be OK.

Oil pressure light is not connected to the voltage stabiliser, it should just be straight to 12v +, then - through the switch. A bad earth on the panel could cause back feed through the oil pressure lamp.

Pressure gauge should go into the switch tapping as this is straight into the main oil gallery from the pump.

[The Swanndri Guy]

Brian, I've checked the oil pressure using a pressure guage, 62 psi at idle and maximum oil pressure of 75psi, with the engine at operating temperature.So the fault is electrical not mechanical. I have also removed the instrument panel, which had a lot of dirt and debris behind it, cleaned it out and refitted it.Since then the 4000 has done 3-4 hours work and the fault has not reoccured.So if the fault ever reoccurs,then I will remove the wiring loom and inspect it and/or replace it. TSG.