Windshield wipers My windshield wipers do not work. My dad has tried to bypass the motor, but that will not work either.

The is the symptom of a defective wiper switch.

Depending on what your trying to do with wipers, I'd want to see voltage on the gray and or purple wire. See the black wire at the bottom that is ground, a good ground is a must. Hey Jeff, I'm not trying to bug you. If I spend time trying to look up info, I'm going to post it. I don't care if the question has already been answered. Have a good day.

its shorted some where from the fuse to the motor
for sure. the fuse saved the fire.
disconnect the wiper motor and fuse.
and use an ohmmeter to find this short.
0 ohms is short. infinity is good, per above setup./
if not obvious the cause, the wire can be bypassed or unwrapped (hard)

check and test the wiper switch and bushings /bearings in the linkages

To troubleshoot car windshield wiper problems, you need to thoroughly investigate problems with any of its operating parts. Here are some of the things that you need to check to determine why are your car windshield wipers not working.

Check Wiper Motor
The wiper motor is the driving force of the windshield wiper. Feel the motor and listen to a humming sound. If there is no humming, the motor is the problem. Check if the motor is working properly and see to it that its electrical connections are made properly. If you find that the motor is dead and beyond repair, get it replaced immediately.

Check For Break in Connecting Wires
The connecting wires of the motor sometimes go loose and that may cause the windshield wipers to stop working. Also check the battery plug connection which the motor has. Connecting the loose wires properly or fixing/replacing the plug might solve your problem.

Check Wiper Switch
Another wiper assembly part that can malfunction is the wiper switch itself. Check for switch malfunction and if you find that is indeed the problem, get it replaced from a mechanic.

Check for Bent Wiper Arms
Bent wiper arms can cause the operation of the wipers to be hampered. If the wiper arms are bent beyond repair, get them replaced immediately.

Check For Blown Out Car Fuse
A blown up car fuse could be the culprit that has stopped the windshield wipers from working. Check the fuse assembly under the dashboard of the car. Replacing a blown fuse might fix the problem of windshield wipers not working.

Windshield Wiper Sprayers Not Working - Things to Check

Sometimes the windshield wiper sprayer stops working which can be very annoying. The washer mechanism is a self cleaning mechanism for the windshield. Here are some of the things that you need to check in case it is not working.

Check Windshield Washer Motor
The windshield washer mechanism might have been impaired due to the malfunctioning of the wiper washer motor. Check if its working and get it replaced if it is beyond repair.

Check Windshield Washer Fluid Level
Sometimes the washer doesn't work because the washer fluid levels are not filled to requisite levels. Filling in fluid might restore normal functioning.

Check For Broken Washer Hose
The connecting washer hose that connects the reservoir to the nozzle, might be broken or worn out stalling the overall operation. Check the hose for leaks and get it replaced.

Check Washer Nozzle For Clogging
Last thing to check is the nozzle of the washer for clogging. An obstruction in the washer nozzle might be the reason for windshield wiper sprayers not working. Using a pin, clean the clogged nozzle. This might restore the sprayer to the normal working condition.

Could be anything but based on experience the probability points to the self cancelling switching in the motor gearbox.

why do you think the motor still works if the wipers don't move? Can you hear the motor run or can you see a little movement when you turn the switch on?

What happens when you activate the washers?

go to a salvage yard that allows you to remove the parts yourself. Then you can see how the motor and linkage assembly comes out.


don't have 1983 info, but here is 1994:

Section 01-16A: Wiper and Washer System, Ranger/Explorer 1994 Ranger and Explorer Vehicles Workshop Manual
DESCRIPTION AND OPERATION Windshield Wiper System, Ranger/Explorer The windshield wipers are actuated by a permanent magnet, rotary-type electric windshield wiper motor (17504) . The two windshield wiper pivot arms (17526) and windshield wiper blades (17528) are mounted on a pivot shaft, one at each side of the windshield. The windshield wiper mounting arm and pivot shaft (17566) are connected to the motor by windshield wiper adapter and connecting arm clip (17531) . Ranger and Explorer vehicles are equipped with an interval wiper and washer (IWW) system featuring a lever-type turn signal and windshield wiper switch (13K359) mounted on the steering column. The IWW windshield wiper governor (17C476) uses a relay contact to control current to the windshield wiper motor . The governor electronic circuitry controls the contact to supply current to windshield wiper motor . A rear wiper/washer system is available on Explorer vehicles. The rear window wiper system consists of a windshield wiper motor mounted inside the liftgate (40010) , an articulating windshield wiper pivot arm and windshield wiper blade , a windshield wiper/washer switch (17A553) and an inline circuit breaker. The front electric windshield washer system consists of a control switch, integral with the turn signal, a windshield washer reservoir (17618) and windshield wiper motor and the necessary windshield washer hoses (17A605) , windshield washer nozzle jet and brackets (17603) and attaching parts.
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Pivot Shafts and Linkage Removal and Installation
NOTE: The left and right pivot and windshield wiper adapter and connecting arm clip assemblies are serviced separately.

1. Perform Steps 1 through 9 of Windshield Wiper Motor Removal as described in this section.

1. If servicing left windshield wiper adapter and connecting arm clip , remove left windshield wiper mounting arm and pivot shaft and windshield wiper blade assembly.

1. Remove left windshield wiper adapter and connecting arm clip access cover.

1. Remove left pivot nut, lower windshield wiper adapter and connecting arm clip and slide it out through left access opening. For installation, follow removal procedures in reverse order. Tighten nut to 10-13 Nm (7-10 ft-lb). Make sure the clip is fully seated in the windshield wiper adapter and connecting arm clip . Do not try to install clip with windshield wiper adapter and connecting arm clip on motor crank pin.
   

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Windshield Wiper Motor Windshield wiper motor are not serviceable. If worn or damaged, the windshield wiper motor must be replaced as an assembly. Removal

1. Cycle windshield wiper blades until in straight-up position and turn ignition switch OFF.

1. Disconnect battery and wiper motor electrical connector.

1. Remove the right windshield wiper mounting arm and pivot shaft and windshield wiper blade .

1. Disconnect the battery ground cable (14301).

1. Remove the right pivot nut and allow the windshield wiper adapter and connecting arm clip to drop into the cowl top outer panel .

1. Remove the linkage access cover, located on the right side of the dash panel near the windshield wiper motor.

1. Reach through the access cover opening and unsnap the wiper motor clip.

1. Push the clip away from the windshield wiper adapter and connecting arm clip until it clears the nib on the crack pin. Then, push the clip off the windshield wiper adapter and connecting arm clip.

1. Remove the windshield wiper adapter and connecting arm clip from windshield wiper motor crank pin.

1. Remove nut and ground strap.

1. Remove three attaching nuts from windshield wiper motor. Remove the windshield wiper motor .

Installation

1. Position the windshield wiper motor and install the three attaching screws. Tighten to 13.6-19.0 Nm (10-14 ft-lb).

1. Install nut and ground strap.

1. Connect wiper motor electrical connector.

1. Install clip completely onto right windshield wiper adapter and connecting arm clip. Make sure the clip is fully seated. Do not put the windshield wiper adapter and connecting arm clip on the motor crank pin and then try to install the clip.

1. Install the left windshield wiper adapter and connecting arm clip onto the wiper motor crank pin.

1. Install the right windshield wiper adapter and connecting arm clip onto the wiper motor crank pin. Pull the windshield wiper adapter and connecting arm clip onto the crank pin until it snaps into place. The clip is properly installed if the nib is protruding through the center of the clip.

1. Install the right windshield wiper mounting arm and pivot shaft and nut. Tighten the nut to 9.5-12.5 Nm (84-110 in-lb). NOTE: When the battery has been disconnected and reconnected, some abnormal drive symptoms may occur while the powertrain control module (PCM) (12A650) relearns its adaptive strategy. The vehicle may need to be driven 10 miles or more to relearn the strategy.
   

1. Connect the battery ground cable and turn the ignition switch on. Turn turn signal and windshield wiper switch off so windshield wiper motor will park, then turn ignition switch off. Replace right windshield wiper adapter and connecting arm clip access cover.

1. Install the windshield wiper mounting arm and pivot shaft and windshield wiper blade assemblies on the pivot shafts to dimension X. Dimension X is the distance between the centerline of the blade saddle and the top edge of the cowl top outer panel grille. The value of Dimension X for each vehicle is given in the Dimension X chart in the Specifications portion of this section.

1. Test the system.

YOUR WIPER MOTOR COULD HAVE BINDING LINKAGE AND PIVOTS.TRY LUBRICATE THEM WITH WD40.TRY NOT TO GET ANY ON WINDSHIELD.IF THIS DONT WORK WIPER MOTOR COULD BE FAULTY.

• Windshield Wipers Continue to Run When Turn Signal and Windshield Wiper Switch Are Turned OFF

• Damaged turn signal and windshield wiper switch .
• Damaged windshield wiper motor .
• Damaged windshield wiper control module.

Pin Number Circuit Circuit Function 1 57 (BK) Wiper Motor Ground (Park) 2 28 (BK/PK) Wiper Module to Wiper Motor (Park Switch) 3 65 (DG) Wiper Motor Power (Park Feed) 4 61 (Y/R) Wiper Motor Common (RUN) 5 56 (DB/O) Wiper Motor LO 6 58 (W) Wiper Motor HI
Windshield Wiper System The windshield wiper system consists of :

• Windshield wiper motor (17508) (F-type).
• Washer system.
• Windshield wiper control module.
• Turn signal and windshield wiper switch (13K359).

The windshield wiper control module is:

• Located at the instrument panel fuse panel.

The windshield wiper motor is:

• Attached to the cowl top extension (021A36) .
• Connected to windshield wiper mounting arm and pivot shaft (17566) .

The turn signal and windshield wiper switch features a:

• Rotary wiper switch.
• Push type washer actuator.

OFF/Low/High Speed

• Has a two-speed, permanent magnet, three brush electric windshield wiper motor .
• The windshield wiper motor has a brush rigging that permits selection of low or high speed.
• When the turn signal and windshield wiper switch is in the LO position, the common brush and the blue/orange wire brush are used, and the windshield wiper motor operates at low speed.
• When the turn signal and windshield wiper switch is in the HI position, the common brush and the white wire brush are used.
• In HI position, electric current will bypass a portion of the armature winding causing the windshield wiper motor to operate faster.
• When the turn signal and windshield wiper switch is moved to the OFF position, the windshield wiper motor will continue at low speed until the park switch outer contacts open.
• When the park switch contacts open, the windshield wiper motor stops in the park position.

Interval
When the turn signal and windshield wiper switch is in the interval position:

• The wipers make single wipes separated by pauses.
• The rotary switch is on the end of turn signal and windshield wiper switch .
• The length of the pause can be set from approximately 1 to 17 seconds.
• Length of pause decreases as the rotary switch is rotated away from off.
• Length of pause increases as the rotary switch is rotated toward off.

While in the interval wiper mode:

• It is normal to hear a slight click at the beginning of each on/pause cycle. NOTE: When using interval wipers, the first wipe may not occur until after a pause of up to 17 seconds.
  

If this MB is built like others I have known, this is going to be a chore. Some models required the removal of the dashboard to replacement the wiper motor. I recall hearing from a frustrated owner (former brother-in-law) that the dealer-estimated labor time was 5 hours.
I wanted to refer you to Chilton or Haynes for an aftermarket manual but surprisingly, neither of them offer one covering your 1990 year.