just a quick update. it was the oil pump, i just primed it and everything going. thanks for all the help

Might be a lot of things.

someone told me that it might be the oil pickup thats got a crack in it.

Yeah like DD said hook up a external pressure guage, standard light only registers about 5psi below anyway, enough so you know you've basically destroyed your motor, you want about 20psi at idle and about 10psi for every 1k revs after that.
Might need to prime the pump, I know aiden on here had that issue and had to fill the pump with vasoline first to allow it to start pumping. You should have oil pressure before the engine fires, pull the coil wire and crank it over.

Use an external oil pressure gauge to double-check. Maybe something wrong with the pressure sensor.

the seals is fine, it's a 1400 bottome end, new pistons, rings, big end, mains, 1200 gx head with new valve seats, valve guides and scemed, new gasket sets (at this stage 3 of them). had engine out 4 times and problem still there. checked bearings, all in the right place and right size

Rear main seal,there are some incorrect seals(too short)floating around in some of the rebuild kits lately.

There is probably another gallery plug missing somewhere. Perhaps inside the engine, it just runs down into the pan.

i installed a new welch plug, installed both front and back oil gallery plugs and the oil leak is sorted, but i'm not getting any oil pressure. i'm using thegx oil pump, 1400 and 1200 seems the same

okay, so i put both the oil gallery plugs in. new oil censor, but no oil pressure. any help?