it would be a big mistake to start working on a motor without knowing what is wrong with it!
1st check oil pressure sensor by grounding oil sensor. if the
light goes out then that wires/system is ok.
then u r down to bad sensor or bad pump/loss of pressure.
if light
stays on then u have problem with wires/electric system and probably not a problem with the oil pressure.
is oil sensor good or bad ?
did you make sure u have oil in the oil reserve tank (no oil = no pressure.)
the last time i changed oil i had the idea of a fast oil change so i removed the filter and started the motor and the flow was good
it did not reach the front tire. (should have the fast oil change perfected after a couple more changes.

i would at a minimum make sure the tank is full and pull the filter and start see if it pumps. (a bout 3 seconds then turn off)