How can I test for a faulty oil pressure sending unit

I have been banging my head for the past few months - replaced the fuel pump/wire pig
tail with AC Delco ( and new fuel filter ).  Worked for a few weeks - then no
pressure/juice to pump.  Dropped the tank/reinstalled pump ( just in case there was a
short somewhere ) - worked for a few weeks then no pressure/no juice to pump.  My
questions is this - would a failing / faulty oil pressure sending unit cause kill the power
to the pump and how would I know if this is the problem.  is there a way to test this
before removing the distributor cap / replace unit.  One other tid bit / I have noticed
while running the oil pressure fluctuates quite a bit at idle after the engine warms up  /
sometimes dropping low enough to almost stall..   Any ideas ./ advice?