The oil pressure light on my 2004 nissan xterra stays

When you get your oil changed they can do that. If you change the oil yourself, I don't know how to do it.

there will be an oil pressure sender unit attached to an oil galley in the block
sound like it is that or ma bad connection for the wire

Sounds like you may have accidentally pulled the wire loose on the oil pressure switch. Just check it to see if it's tight and not broken or stretched..Always try easiest fix first..

It's located by oil filter,may have to remove filter to remove switch,may need a stubby(short) wrench to remove,may be able to turn tiresout to get to,it's a tight fit.Remove electrical connector,then get wrench and remove,then take to Autozone and match up with new one,here it is. Duralast Oil Pressure Switch PS561 2006 Nissan Datsun Xterra 2WD 6...

Click the link below :----http://wikisolutions.blogspot.in/2012/02/get-free-answers.html

1st you need to do an oil pressure test. If it reads between 20psi-60psi, then it's Ok and you have a bad oil pressure switch. If it's below the above specs then you have an internal engine problem - IE: bad oil pump, bad bearing, etc...

take your vehicle to your locale autozone, they do free diagnostics tests. They'll tell you what codes your vehicle is sending out(Plus alot of information about that code, what needs replacing)
Good luck

the engine may be slugged up from lack of maintenance/oil changes, since the oil was black when you purchased the truck. was the light coming on before you changed the oil?? if not, try changing the oil filter for nissan one. if that doesnt do it than you can dump some internal engine cleaner into it if you want, but it may develop external oil leaks. the oil builds up a film after a while inside of you engine. if you wash it off, the engine may start leaking oil. to really diagnose this, you should take oil pressure reading at the oil pressure sending unit. you will ofcourse need some specialty tools to do this job such as pressure gauge and oil pressure sending unit socket to remove it so you can screw the gauge into it.good luck.

The oil light comes on when there is no pressure. There is no pressure when the pump either cannot get oil to pump or has oil and will not pump it.

Get it checked before you do anything else. A engine running with no pressure is a cooked engine.

9 times out of 10 it is nothing. My engine light stays on. If it really bothers you then you can take it to any oil change place and there is a sequence that they do.`