Low oil pressure reading on ´96 Toyota T100

Its located behind the distrubutor its pretty easy to get a

the dodge web site shows it. there,
as does the shop manual shows it.

a 2004 toyota highlander V6

this should be your engine type
The 2GR-FE is a 3.5 L (3456 cc)

if leaks are that bad
always check the engine oil level before you drive off

fixing oil leaks on motors
degrease whole motor top and bottom

start with replacing the oil sender it may be the cause of the oil light coming on
after degrease
lay cardboard or paper under the car
take out for a drive and park over the paper over night

this pin points most of the oil leak locations
leaks from a V6 motor
rocker covers/ spark plug tube 0 rings.engine seals
cam seals
front and rear engine seals leak often
sump gasket can leak

if oil consumption or light on continues
can be a failing engine oil pump
or worn main bearings giving low oil pressure to the whole engine
you could be burning oil from worn piston rings
or hardened valve stems

a mechanic can fit an oil pressure gauge to the motor when hot
to check running oil pressure to confirm low oil pressure

if engine is worn out

it is possible to fit a lower mileage used motor to your highlander
its often cheaper than and engine rebuild

Its called that one piece so you can't speed or rev so high that you can blow it up... hmmm the govener

Could be your oil pressure switch,here's a link.http://www.autozone.com/autozone/parts/Duralast-Oil-Pressure-Switch/1985-Toyota-MR2/_/N-ijxzlZ8znc6?itemIdentifier=261416_0_8450_ Here;s the location.http://www.autozone.com/autozone/repairinfo/componentlocations/componentLocationMain.jsp?fromSearchPage=true&categoryNValue=4294963411&categoryName=Oil+Pressure+Switch

You might have. But it could be the sending unit, or the guage. You could take it somewhere and get a guage hooked directly to it if it's a real concern. On the other hand, it could be just fine. And if it's not knocking or burning oil, I wouldn't worry about it.

I also have a '95 T100, which also 'appears' to have low oil pressure. This is a commonly reported issue, which apparently isn't a problem. Do a search on YouTube for 'T100 oil pressure' and you'll see others comments regarding this.

Most likely the fuel pump is failing, the fuel pressure check valve is defective and the system loses pressure the long crank is due to this loss of fuel system pressure.

GM oil pressure senders have a pretty high failure rate. Since your van is over 10 years old, and pressure senders are not too expensive. 
I would start by replacing your sender...there's a pretty high likelihood that you will eventually replace it anyway. Change the oil and filter every 3000 miles and use a 10W30 with a Lucas oil treatment and with a can of Restor would not hurt ether.
Getting to expensive to buy and replace a good running van over some light routine mantance for around $20.00 every 3000 to 5000 miles.
Good luck and hope this helps.

I think you have a bad ground on your engine gages...but, more importantly, have your oil pressure checked by a mechanic.  If it is indeed only 20 pounds the engine is sadly on it's last legs.
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Take a gauge and check you oil pressure. If its not low then change the pressure sensor. If the pressure varies and the pressure is not where it is supposed to be, then drop the oil pan and look in the bottom of the pan. If you see slivers of metal then the bearings are going out. Eather the cam bearing, rod bearing, or main bearings.