My grandmother has a 1998 Lincoln Town Car and her windshield wipers only work sometimes. like she will leave her house and try them and they wont work then she will get back in her car sometime after and they will work?
My guess is that on that car, the wipers are controlled by one of the electronic modules. Some basic troubleshooting is a good start, such as making it fail, and testing to see if you have power at the motor. Also check the fuses.
If there's power at the motor, then it may be the motor. Remember it is a multi speed motor, so one speed may still work.
Also note that there is an interval governor function (delay box) also controls power to the motor when in that mode. It should be in the same electronics that control the wipers and washer. I am not sure but there may be a relay to power the system due to delay when shutting the car down, like the lights. If so, check it.
Painful, but some testing is in order, as opposed to parts changing, I would think, as this system has a good bit of controls.
Probably the wiper switch, although it could possibly be the wiper motor (bad connection or intermittent internal short) and/or a bad ground. Maybe pull the plug to the motor, clean the contacts if necessary, and see if that helps. See if the motor is getting voltage when you switch the wipers on - if so, then the motor assmebly is crapping out; if not, then the switch and/or relay is on the fritz.
You may try posting this (or have the mods move this) thread over in the Non-Mustang Technical Forum.
First things first, remove the multi-function switch (wiper switch) and inspect all the wires going into the hard shell connector. It is the same connector as the Mustang and suffers from the same problem. The little plastic "hooks" that hold the wire pins in the connector tend to break over time and allow the wire to get loose and in some cases, wiggle all the way out.
Remove the switch and make sure there are no loose wires on the back, going into the connector. Just simply pull gently on each one to see if any of them pop out. If so, go to your local Ford, L/M dealer and get a "multi-function switch hardshell connector", they will know what you are talking about. Use a small pin or hook to pull back each hook in the connector and remove the wires, one by one, and place them in the new connector in the same locations.