oil warning light when cold

please help as i am propper stuck. 1.8 8valve mk1 gti. start it up when cold all ok, drive when cold as soon as you hit 2500 revs oil light and buzzer start going crazy. after less than half a mile goes off. if i let it warm up a couple of minutes before driving then drive it its spot on.i have put bigger pistons, ported,pollished,cam ,etc. but i dont see how this would make a difference. all the bottom end bearings have been replaced. oil pump replaced. oil pressure sensors replaced.the engine has just been rebuilt. i havent replaced oil temp sensor yet and i dont know which sensor should be where on the filter housing but i dont see how the position of sensor would cause this problem.my mfa also doesnt work so i cant reed the oil temp,not sure if this could be part of the problem. sick of chucking money at it and wondered if any of you guys and gals had suffered a similar problem
any advise would be of help         chears deanos

Got the wiring on correct positions in bay? If you have a meter try connecting it up to the one sensor wire at a time and have a passenger read it while your driving, could be it's picking up a signal from another sensor. :dontknow: Using the correct oil & filter  :dontknow:

Will try that this weekend.Genuine filter has been used.Did have 5w-30 oil in and thought that might be the problem so dropped it and used 10w-40 oil but its still no better.

Although the oil is not the problem, don't use oil that light as these engines were designed with 1970/1980 standards and not modern day tolerences. 10 weight should be the lightest you use unless you live in the Artic.

As you just rebuilt the engine then it is possible a small piece of crap got itself stuck in the high pressure switch, that is the one which sets off the light & buzzer. It is the one located on the oil filter mount and you could test the wire there for a break also. The instrument cluster has an oil warning system mounted inside and they have been known to go bad from time to time. 2000 - 2500 RPM is when the warning system will trigger the light and buzzer if it is bad, or you have a real high engine speed pressure problem. So if the wiring and switch are OK and you know you have good pressure, only way is to test it, then the dynamic oil pressure warning system is defective.