My oil pressure light came on we changed the oil but it still comes on what do i do next

1. As a basic measure I would make sure the correct grade and spec oil is going in the engine. You can no longer trust that a local mechanic or even a dealer service center will necessarily use the required product as stipulated by the manufacturer. It is always better to buy and supply your own so you know the correct product is being used.

2. I would not assume there is a problem with the oil pressure warning light even though there could be.
The first thing the mechanic should have done when you reported the oil pressure issue is to hook up an independent mechanical oil pressure gauge and check oil pressure when the engine is hot at different RPMs. Any oil pressure issue will usually show up at idle when the engine has been warmed up properly and the engine oil is hot (unless you have some kind of intermittent oil pressure relief valve that is sticking). Just replacing parts without actually knowing what the oil pressures are at different RPMs is being sloppy and negligent.
This is what you need to do now. Contact a business that can hook up their own pressure gauge to your engine and have them check the oil pressure readings at various RPMs when the engine is fully warm. If there is a low oil pressure issue it will show up on the oil pressure gauge. As you have a new oil pump there should be no issue now with oil volume or a sticking oil pressure relief valve which on your engine should be part of the oil pump assembly.

3. Worn engines will not be able to sustain required oil pressures. Oil pressure is not produced by the oil pump. The oil pump produces oil flow but the resistance to flow is what produces the oil pressure and that resistance is created by fine clearances between operating engine parts especially on the crankshaft and components connected to it. Once the engine wears the clearances increase and the oil flows past the parts much more easily and produces/builds much less pressure.
How well your engine with over 90000 miles has been maintained depends on how often all the owners changed the engine oil and filter , whether they kept the engine oil level up to full (most owners rarely ever check oil levels between services) and whether they always used the correct product. Manufacturer oil change intervals shown in service schedules can be 10000, 12000 miles or more which is much too infrequent for the type of use 95% of private vehicles experience which typically are on the severe to very severe use end of the spectrum. Engine oil typically needs to be changed at least at half the mileage shown in service books (at least twice as frequently) and thus at least every 5000 miles if you want your engine to last.

Well it could be a faulty sending switch, or the pressure really could be low. A mechanic would use a mechanical gauge to verify the problem.
If it is low oil pressure, you may need another engine.

anything less than 15 psi is low... and this is for all automotive engines

The oil pump is the next step.
It could be bearing or other things like blocked return flow that did not come out with the flush, bearings on the cam shaft etc.

Next thing I would check is the oil pressure switch. I have put two of these in my wife's Park Ave. They are 40 bux for the lifetime warrenty one.

REmove the wire from the sender unit and earth on the engine next to it. If the light dosen't come then it is probably blown or you have a fuse problem in that circuit

which oil sending did you change .there is 2 on that motor. 1 is next to the oil filter and the other is in the oil pan next to the oil plug

Oil pressure is always lower at idle speed.I'm guessing you have high mileage.If your oil light is not coming on in drive at idle with the engine cold,but it does when hot,your bearing clearances are probably getting a little loose.Try using one quart of Lucas oil additive in place of a quart of oil at your next change(or just change it now).This stuff is thick and stringy,it helps the oil cling to surfaces.(if there is no change after this,you could try a new oil pressure switch-it's cheap enough.I actually had the switch on my 95 dakota leaking a LOT of oil at high pressure/RPM,which affected the reading).

1. Check your oil level. If oil level is not ok, correct oil level and find out why oil level was low and correct the problem. (Leaks, bad PCV, Burning oil due to severe engine wear, nobody has bothered to check it for the last 3000 miles, WAY overdue for an oil change, etc.) If oil level is ok, proceed to next step.

2. Remove the oil pressure sensor and install a manual oil pressure gauge. Run engine to verify low oil pressure. If gauge shows that the oil pressure is low, overhaul or replace engine. If oil pressure is ok, replace oil pressure sending unit and retest.

this is due to low oil pressure. i would do an oil change and get an oil filter from the dealer(actually you should be able to get motorcraft filters at any parts store) but dont use fram. up grade your oil to the next heavier weight( 10w 30 go to 10w 40) and see if this make a difference. if no difference is noticed the next diagnostic step is to see your technician and have himperform whats called a wet oil test. by this i mean that the pressure sesnor is only taking pressure and converting it into an electrical signal which if the sensor is bad..... so he takes out the sensor and replaces it with an actual gauge to read pressures. this is the most acurate way to test. from there he will be able to advise you on the next step of repair.