I have a 2000 Ford escort zx2 and the other day i shut the car off and the oil light came on ,, it is not on while the car is, it comes on when i shut off the car and stays on even with no key in. I have to disconect my battery every time i shut the car off so it won't die. any any any idea what this could be? diagnostic check came back with nothing! :banghead:

My guess is that one of the relays normally controlled by the ignition has gotten stuck in the 'on' position. There wouldnt be one just to control the oil light by itself, so something else might also be on - like the PCM, or the ignition 'igniter' or even the fuel pump. In this situation the oil light comes on because the oil pressure is zero with the engine stopped.
We have a 92, which has a box full of various relays & fuses, located under the hood & near the battery. With the battery connected - and the oil light being on - I would pull the relays out one at a time, and check whether the light goes out when one of them is pulled. You could do the same thing for the fuses under the hood. If the light Still stays on, try pulling the fuses that are located in the car, somewhere below the dash. Usually not a convenient location! If you can isolate what circuit it is that is involved in keeping that light on, you will have some idea where to go for step 2.
The other possibility could be a wire serving the oil pressure light that was shorted to another one of the wires in the harnesses feeding the instrument cluster.
Ford published good Service Manuals for the Escort, with a companion manual for just the wiring. At least they did in 92, and I got a set from ebay for about $50. They are so detailed they are a 'slow read', but you can follow any circuit in the car, given the time to read up on it. Also good for going to sleep for an insomniac.

Could be a problem with the ignition switch.