windstar door wont lock

i have a 95 windstar slideing door wont lock at all with or without key can any tell me what to check

There are four contacts on the door at the front... use a red eraser or very fine emory cloth to polish the crud off of the contacts both on the frame and the door. If you have some dielectric grease or TV tuner cleaner, treat the cleaned contacts with one of those... that will likely solve your problem.

There are four contacts on the door at the front... use a red eraser or very fine emory cloth to polish the crud off of the contacts both on the frame and the door. If you have some dielectric grease or TV tuner cleaner, treat the cleaned contacts with one of those... that will likely solve your problem.
I tryed the earser that didnt work so i'll try the others thanks

If you are saying the door can't be locked even using the inside locking plunger knob.... then I would guess a linkage has "come undone" inside the door trim panel.

Does the door lock and unlock when the door is open? This would point to a door alignment problem. Does it lock and unlock with the knob? The knob uses a different linkage than the cylinder. If it won't lock or unlock from the knob, cylinder, or power locks, then it points to a door latch sticking. You could try spraying brake clean on it since it will remove dirt build up but not leave a residue to attract more dirt but if it is a latch, you'll probably need to get it replaced. Good luck with it.