oil light

ok, i'm new at this. so here i go, i just bought a 81 kz550 i beleave it's a C3. any ways its my second bike my frist being a 09 ninja 250, being a 09 i never had to do any work to it i am pretty good with cars and what not and never had any real problems turning a wrench. but my problem with the kz550 is after the bike warms up the oil light kicks on after it gose below 3500 rpms. what is was wondering is how often do the switch/sensors go out or if i need to change the oil pump

Did you look at the oil level

yeah oil leave i checked that, i even changed it thinking the filter might be old but it didn't help any.

I'd buy or borrow an oil pressure gauge to see what the pressure really is. That will tell you if it's a sensor or if the engine has serious problems.

ok well oil pressure isn't something i've ever had to deal with any tips where to start. meaning is there diffrent types of gaguges if so what kind should i be looking at to get and what should the oil pressure be running at