Rear wiper won't shut off

There are two insanely unreliable computers involved in running the rear wiper. The HVAC controller with the control switches sends a coded signal to the Body Computer which has a very high failure rate. Start by replacing the Body Computer as a test. You might want to leave that to a professional as it is very difficult to remove. It's plugged in and bolted in front of the brake pedal.

I'd still suspect the Body Computer based it its history of causing problems with the front wipers. I'm sure the rear wiper circuitry will be the same.

There's three 5/16" or 10 mm bolts holding it in. I can't remember if there is also some type of latch, but the module will pull straight down. The hardest part is reaching up there to find those bolts. Use the replacement module to look at the locations of the bolt holes.

Does your van have the factory-installed anti-theft system? I don't recall if this applies to the minivans but the Intrepids can use any Body Computer or Engine Computer from any car if it has factory anti-theft. If it does not have that system, you MUST install a used Engine or Body Computer from a car that also did not have anti-theft. If either computer has that upgrade programming it will teach it to the other one when the ignition switch is turned on. At that point both computers will require a "disarm" signal before they will work. That signal is never coming if the car doesn't have the anti-theft system. That upgrade programming can not be undone so both computers will have to be replaced at the same time before the engine will start. Again, I don't know if that applies to the minivans but it's a big source of frustration for Intrepid and older Neon owners. If you DO have the factory anti-theft system you might just have to relearn "minimum throttle" before the Engine Computer will know when it must be in control of idle speed. Before that is relearned you will not get the nice idle flare-up to 1500 rpm for a couple of seconds when you start the engine and it might only stay running if you hold the gas pedal down 1/4". That relearn procedure should only be necessary if the battery was disconnected or run dead. To relearn minimum throttle, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals. The only minivan Body Computers I ever replaced were at the dealership with new computers. I didn't have to be concerned with the anti-theft systems because the module would work right out of the box on vans without it, and if it needed to be programmed for anti-theft, that happened automatically from the Engine Computer when the ignition switch was turned on for the first time.

Nope, you have that backwards. No need to send it back. Since your van has anti-theft, that module will work just fine. Because you already installed it in your van, it has self-programmed itself to only work with vans with anti-theft. It learned that programming from your Engine Computer when you turned on the ignition switch. It won't work in any vans without anti-theft now.

Oops. I have to modify my story. I only have a '97 service manual but I'm pretty sure the system is the same for '98. According to the manual, you must open the hood, then unlock the lift gate with the key. That will initialize the anti-theft system in the Body Computer and should allow the engine to start. Only the lights will flash. There won't be any horn when the anti-theft system is triggered until the engine has been started 20 times. I like this procedure better because it means you don't have to worry about where the used computer came from. Hope that works.

I assume it's going to have to have the switch inside. If it doesn't, there might be a pair of wires in the harness that can be connected to a switch that can be operated manually.

Do I understand that you can turn the lift gate lock cylinder both ways for "unlock" and "lock"? On my old stuff I can only turn it clockwise to pop the latch. The wire you want is a 20 gauge white / red in the left connector. It needs to be momentarily grounded, but it's not that simple. There are two resistors inside the missing switch. The Body Computer sends a voltage out on that wire, and that voltage will change depending on the value of the resistor that is switched into the circuit. Typically they will send 12 volts out there, but it could also be 5 volts. It's irrelevant to the story but if we use 12 volts for the description, there are four possible conditions. Full 12 volts will be seen on that wire most of the time. If you ground it, there will be 0 volts. When you turn the switch to "lock", one resistor will be switched in and there may be 8 volts on that wire. In the "unlock" position a different resistor is switched in and there might be 4 volts seen on that wire. The 4 and 8 volts are interpreted by the Body Computer as the "arm" and "disarm" signals. There's a 99 percent chance grounding that wire would not cause any damage but most likely that will not initialize the anti-theft system either. You need to ground one end of a resistor, then momentarily touch that white / red wire to the other end of that resistor. The problem is they don't say what the values of the resistors are. There is a separate diagnostic manual for the anti-theft system that would have those values listed in the switch testing section. Is there any chance you still have the old lift gate? If you do you could read the resistor values with an ohm meter, then you would know the value of the resistor to use. From my limited experience with cruise control circuits, 560 ohms, 2200 ohms, (2.2k), 10,000 ohms, (10k), and 18k are typical values. That's how the computer can tell the difference between four different switches when only one wire goes to the switch assembly.