Signs of oil pump failure...
 

I have a M104, that has a wacky oil gauge (i know that i need to replace the oil pressure switch) anyways is there any signs that the oil pump gives when its about to fail (sound, engine performance problems...) if so what is it... What oil pump method dose is use, gear pump, eletrict pump???.

The oil pump is chain driven, change your oil sending unit and it will be fine.

I agree.

so the chances of that oil pump of failing is slim??? It looks like a tight fit to get the to the oil pressure sender out and in

Oil pump failure is extremely rare. There's a very good chance it's either the sending unit or problems with the lower engine harness.

The entire wireharness has been replaced by mercedes dealership, i guess i have to find a way to remove that sender, do you remove the sender under the car, it looks like that's the only way am i right...

What we're talking about here is a second harness. If they replaced only the engine harness there's a pretty good chance your lower harness is original and a suspect.

Yes, under the car is way easier.