i have changed the water pump thermastat,heat sencer,heat sending unit

If you have the cooling fan on at all times and it still over heats, you have a bigger problem. I would go to the auto store and buy a block tester. It's just a plastic tube with a chemical that you add. This way you can rule out a bad head gasket. Plenty of videos on youtube on how to do the block test. Is you system pressurizing? Are your hoses hard when hot? If not, replace radiator cap. Next I would buy an air bleed kit to make sure that there isn't a large air pocket in the system. If it still overheats, your radiator must be plugged with rust. You have pretty much changed out everything else.

This is not a link to a wiring diagram, but I think you have more than an electrical problem. Since you say the fan is running all the time, I think you have cooling problems. The car is 18 years old. There is a good chance that you need to have your radiator rodded out (overhauled) and flush the block until clean water comes out. Then when done with both of those install a new thermostat, refill the radiator with the proper ratio antifreeze. Get your fan to work properly and that should take care of the problem.