I have a 1988 ford f150 and my oil pressure gauge is below half,does this mean my oil pump is finished.

Since you already know what your physical oil pressure is at idle I would try to get an accurate spec from Ford. if 10psi is normal the the problem is likely the switch or cluster.
If it is below spec it could be high mileage (normal bearing wear will lower idle pressure) a weak bypass spring in the pump, or a the wrong oil filter or oil.
If you are not hearing any "lifter clatter" or knocking when u start it, I wouldn't be too concerned about a bad pump or engine damage just yet.
Use only 5/30 or 10/30! anything thicker can cause cam damage due to oil starvation. Also going to long between oil changes can lower idle pressure as the oil looses viscosity and thins out.
According to factory wiring diagrams 2001 F150 does not have a pressure gauge , it has a warning light, however when I read the test procedure it talks about a gauge. either way, light or gauge, it uses a switch (not a sender) to signal the cluster that oil pressure is either above or below a certain value. again, I'm sorry, i don't know what that value is.
The instrument cluster receives ground through an oil pressure switch. When oil pressure is above a certain pressure the switch closes and the instrument cluster then turns out the light or indicates "normal" oil pressure. if the pressure is below a certain value the switch is open (the circuit to the cluster is not grounded) and the light will be on or the gauge will read no pressure.
The light or gauge is NOT directly controlled by the switch. If it has a gauge the gauge will show an increase in pressure when engine RPM increases (calculated by the cluster) it is not showing true pressure.
if your idle pressure is normal, you can test the by grounding the circuit at the switch, key on, if the light is out or the gauge reads normal the problem is the switch (assuming that physical pressure is above spec).
If the idle pressure is slightly below spec you could try an oil stabilizer like Lucas or STP and keep your oil change intervals to 3500 miles.
I hope this helps, feel free to contact me for more information

Robert Grove, ASE Certified World Class Technician, Automotive Hall of Fame 1996
Wego2u Mobile Mechanic
Mobile Mechanics in Orange County, CA

By the oil filter is the oil pressure switch,screwed into block.If you have a oil pressure gauge,it won't work.

The oil sender went bad and the light came on check the oil 2 times engine running observe oil level and engine off observe oil level if when running the oil level is higher the oil pump is working and your ok and the sender failed or dirty connections if oil level is the same on both checks oil the pump is not working and needs to be replaced

I assume you mean "Oil" pressure...This is the first sign of the main bearings getting to the point of needing replacement. The fact that the pressure goes up when you accelerate tells me that the oil pump is working. There is just too much bearing clearance for the oil pump to keep enough volume flowing at idle to maintain pressure. In short, it's time for an overhaul. It will be less expensive if you do it now than if you wait until you spin a bearing and destroy a crankshaft, or put a rod through the side of the engine block.

could be but have you actually check the oil pressure

The oil pressure gauge on your dash is really just an warning light and you are not really looking at real oil pressure

Therefore you could have an electrical issue, mainly high resistance in the sender circuit that make the gauge read lower than actual

Remove the oil pan and replace the oil pump.

check gauge connections, more often than not it is a faulty/not connected gauge

How many miles on it? Could be the oil pump if the oil level is full.

If low oil pressure is verifiable the only repair is replacement of the oil pump assembly.

Start by verifying oil pressure with a mechanical oil pressure gauge. If oil pressure is low then replace oil pump.

You can pull the oil pressure sending unit and install a mechanical gauge in the hole, and check if you have pressure, is so you can replace the sender, if not you have oil pump problems.