yeah i'd expected unless there's a computer thingy that would light a dash light from a low pressure reading in the extra panel, it wouldn't have had an oil pressure "manifold" for the sender AND switch on the engine.. I've seen enough engines to know they only come with one or the other.
you could put a T piece fitting in the block and run both, 

you also shouldn't be too worried if the oil pressure is on the low side with an engine with close to 300,000kms,  I've had them idle with the light flickering or the gauge reading low on several clapped out crossflows, they don't die, they will more than likely easily do another 100,000ks without oil issues.. when they are worn out they usually wipe a lifter lobe or just burn a heap of oil from either rings, glazed bores or worn valve guides etc. (they very rarely failed to run, i fitted a second hand lifter to one of My engines every few months from a wiped out cam lobe before eventually swapping the engine. doing about 800km per week at the time.) 
if the gauges reads enough pressure not to flash, or the switch type put the light out, good enough was good enough for a standard daily car. 

Got a sender off ebay that seems to work but my oil pressure situation doesnt look too good so Ill be hooking back up the mechanical gauge to get a better look. I cant figure how the factory light would have been wired with the sender so it must have just omitted it for the ghia aswell.

you just need an oil sender from a ZL fairlane or S pack XF or even the XE s pack/ghia oil sender will work, 
EA to ED (extinct basically will also work but are slightly different range, i can't remember if they read higher or lower oil pressure by a small amount but it's negligable)

there was no oil light on S pack, but possibly Fairlane ZL or LTD FE may have had some extrapolated thing in the trip computer extra gauge on the dash (were 2 types, one was just a bunch of lights, the other a trip computer.. won't fit in a standard dash though..

 you could probably tap into one of the unused light positions on the fairlane cluster, i can't remember what they had.. radiator low level was one of them, use that as an oil light spot if you wanted to keep the on/off oil light. may be others also (shine a torch in the globe holders and see what lights up) 

Well shit, got the dash in and when its hot it starts flashing and to top it all off I had to pull the oil pressure light as due to the new sender it wont go out and messes with the readings. Anyone with one of these clusters or a car that came with one know if they came with an oil pressure light? Maybe it was omitted due to the gauge

Hard to see on camera but the bottom line is noticibly dimmer on one side and has deterioation around the cathode wires so I have some hope

Could be the fuel cut off solenoid

It happens on the ghia cluster also, oil pressure reads max and volts start flashing. Im guessing it has something to do with the stray earth caused by the sensor switching off. Im also exited (and slightly nervous) for the vfds aswell. The process involves pumping an increased voltage into the cathode wires to burn off any impuritys or oxidation, this runs the risk of killing the vfd if you put too much in so you have to be very carefull and a bit lucky but it can help brighten them significantly and fix dark spots. Ive got the tacho apart and it doesnt look like anythings wrong so im just gonna clean the connectors and send it but Ill drop a before photo for the vfds after work

yeah they share the same warning flash.. (if it's got low oil pressure it will flash, or if it's got a battery issue it will flash.)

it always annoys me when you see these high series clusters for sale and they haven't included the oil sender.. (it's fine if it's for the same spec level car, but retrofit = annoying and difficult to track down the senders, cheap at least) 
tacho is likely the needle rubbing on the lense or backing plate in my experience, fragile needles or it's slipped off the pin is another common issue. 
never seen a fix with the VFDs, (never seen an issue with them actually) so it would be interesting to see a pic of the issue before also. 

Found and fixed! My headlights were cutting out and taking the tail lights with them. Turns out not only was my earth bad but the terminals on the circut breaker near the two relays were rusted to high hell, after cleaning them up all was good. Also fixed the volt meter issue with the spac cluster, turns out without the proper sender for the oil pressure once the engine starts and the pressure switch disconnects the lack of earth screws with the voltmeter. By connecting it to earth it reads properly when running. Ive got the sender ordered and Ive got the spac cluster apart to fix the tacho and hopefully rejuvinate the vfds to fix the dark spot in my fuel gauge (Ill upload photos when I do it) so more is coming in the future

Well abit has happened, with starting a new job I havent had the time but have had the money so I took it off the road for a few months and gave it a birthday. Gave up on getting the seat replaced and just got it repaired and reupholstered, while I had it out I added new sound deadening and vinyl floor and took the opportunity to get a full 2.5" exhaust fabbed up by a mate extractors, glasspacks and all. Got the air con working aswell with the original compressor! Just had a peirced condenser. After all that the water pump, welch plugs and heater core sprung leaks so it was another week untill I got it all sealed up but its water tight and alot colder inside this winter. New headlights with plans to swap in the original lenses once I have a free weekend. Got some electrical work this arvo so Ill make this a two parter