Need Advice on disfunctional Windshield Wiper Motor

[FlameRed]

I wanted to ask the collective for advice on my M998, which I just discovered did not have functional windshield wipers. I think it is the motor after a bit of testing.

I found a YouTube that pointed me to a connector on the bottom of the windshield which commonly corrodes. I have a hardtop installed so it would be very difficult to test / replace it as shown in the YouTube

But after doing some tests, I don't think that is the problem.

No noises or motion to the motor with the switch set to low or high.

Here are the tests I ran:

• Found +24V on the connector to the WW switch with the ignition in the run position.
• Found ground on the connector to the WW switch
• Next I ran a separate ground, direct to the battery, and used a power probe to test.
• No sounds from the motor with +24 applied from the power probe and seperate ground to the connector into the switch with the switch in high or low.
• Next I disconnected the plug with 4 wires that goes directly to the motor itself.
• I found ground, and +24 volts and when the switch was turned to low or high, I would see 24V at the appropriate pin.
• Tried to power the motor with the power probe's 24V and no motion or noises at all still.

So I believe the wiper switch is ok based on the above testing.

One thing I found also that might be related is if with the powerprobe applying 24V to the switch directly, if I press the washer button the power probe screams with a circuit breaker resetting message, so I assume the washer pump is broke/shorted also. I assume this is unrelated?

So I decided next step I should remove the motor mechanism for bench testing, before ordering a $400 replacement!

• I removed the three bolts that hold the motor and switch to the windshield.
• The motor popped out and I see an ecentrant arm that is bolted to the motor shaft on one side, and the arms inside the windshield on the other.
• Then there is some kind of bolt that attaches the ecentrant arm to the wiper mechanism.

Which bolt gets removed to pull the wiper motor out? I tired to remove the one on the motor shaft but it would not budge and the arms moved instead. If it is the other bolt, it does not look like there is an access plate on the outside of the windshield to get to the other end of the other bolt. How do you disconnect the wiper motor from the wiper arm mechanisms?

I searched the tech docs, but I guess I don't have the one that has the procedures for the wiper motor.

Also, any suggestions for a replacement wiper motor assuming it is truly dead?

Any help would be greatly appreciated.

 

[Mogman]

Did you try "tapping" the motor with a small hammer? sometimes the brushes get stuck.
It sounds like you have done some good troubleshooting, one thing did you measure 24V and ground with the motor attached?
not sure about the removal but it should be in the TM.

 

[MarkM]

You can find an NOS windshield wiper motor/switch assembly on fleebay for under a hundred bucks. I came up with a fix for the contacts under the windshield. Just liberally spray the bottom of the windshield where it folds with WD40 in the center about a foot wide. I did this to mine two years ago and haven't had an issue since. Mine would work only when it was wet out side. Hope this helps.

Mark

 

[FlameRed]

Thanks for the tips. I will first try the hammer and WD40 soak tricks before I order a new motor.

I did find the service manuals, and it says it is a "clip" that connects that eccentric arm to the wiper arm. Sure looks like a bolt on mine - something with threads, but perhaps I am wrong. Who know what was done to it during the last 30 years.

 

[Mogman]

One word of caution, any oil that gets on CARC paint tends to stain it and is a PITA to get off.
If you have power to the motor there is no reason to soak your truck in WD40

 

[FlameRed]

The good news - it did have a clip and it was fairly easy to pull the clip off.

The bad news - the clip was rusted and disintegrated into a pile of rusty sand and the bushing was all but gone from ware.

Cost of replacement for the clip and bushing? $34

If I would have had some remains left, I would have gone to Ace hardware and matched it up with something generic.

 

[FlameRed]

This just gets better and better.

So the motor I ordered, was supposed to look like my original:

But the one I received, is not what mine looks like:



So I emailed the vendor to send it back since that one I could get for half what they charged me and I don't want to have to drill new holes to mount this! No response. I'll just dispute the credit card transaction tomorrow if I still don't get a response.

So now here is where I really get confused. Maybe someone can tell me where I am going wrong. I take my old motor, and hook up +24V and ground directly from the batteries to the old motor - no motion. Yes, with a VOM I see +24V between the leads.

So I take the "new" wrong motor they sent me, hook up the same leads - no motion on any switch setting. I guess they sent me a bad "wrong" motor to boot?

 

[Mogman]

I would look at the terminal numbers and wires against the schematics again.
One thought I had is when you said you pushed the washer button and caused a short, what if you had the ground and washer wires reversed, you would have 24V on the power lead then when you pushed the washer button it shorted the power to ground but there would be no path for the motor to run.

 

[FlameRed]

I would look at the terminal numbers and wires against the schematics again.
One thought I had is when you said you pushed the washer button and caused a short, what if you had the ground and washer wires reversed, you would have 24V on the power lead then when you pushed the washer button it shorted the power to ground but there would be no path for the motor to run.

Yes, you were correct. The two input wires at the bottom connector are not what they appeared to be. The "ground" I found at the plug, #71 is for the washer motor and I thought it was a ground for the motor. There is a seperate external bolt for lead #57 that supplies the ground. No wonder I could not make the "new" wiper function!

Indeed the old one is dysfunctional. I tried the hammer trick, but no luck. It is really dead as I tested it directly to the batteries using the correct ground this time! I even tried turning the shaft with a wrench with power supplied. The shaft is free, but no luck.

I got really frustrated as I could not reach the vendor so I shipped them back the wrong motor on my dime and opened a dispute on the credit card company. PayPal is absolutely worthless! That got their attention they admitted they shipped the wrong one and offered to provide a return shipping label and they claim the have the correct wiper motor. The call it the "long" style.

Thanks for all the advice!

 

[FlameRed]

I have done electrical work on civi cars for 25 years, but I am stumped!

I voilated the cardnal rule - don't throw (expensive) parts and think it will fix things! Do''oh!

I got a new wiper motor and it behaves the same as the old one under all the same tests I ran. So now I am getting desperate.

Here is the schematic:



I wanted to "bench test" this - to eliminate any wiring problem in the M998 first. My test:

• Lead 57 appears to be ground, and goes to the outside housing and is supposed to connect down to the steering wheel column ground according to the schematic. I connected this directly to battery ground, and confirmed with VOM. Put a fresh bolt on it as the old one looked covered with paint and might not have good contacts.
• Lead 71 is for the Washer, so let's forget about this for now - not hooked to anything.
• Lead 27 is supposed to go to the "Run" position on the start switch and have 24V when in the run position. I hook this up to the +24V battery terminal with a fuse. I see +24V VOM

When I apply 24V to lead 27 (+24V I think) direct from the battery and ground 57 to battery ground, the new and old motor will not move in Low or High position.

But here what is puzzles me.

When I press in the washer button, the resistance between lead 71 (washer) and 57 (ground) goes from infinite to 0. All good - as expected.

• When I have the wiper selector switch turn to "off", and I measure the resistance between 27 (24v) and 57 (ground) I would expect the resistance to be infinite. No, it is a few hundred ohms, on both motors! In no switch position is the resistance between 27 and ground ever infinite. The motor cannot always be plugging current - can it?
• When I rotate the selector to "low" or "high", the resistance between 27 and 57 goes up slightly.

Another question. In the schematic I show above, the have a circle around all three leads, 27, 57 and 71 and labeled it "Jumper" - not sure what that means.

So which leads sould get +24V direct from the battery, and ground to the batteries for the motor to spin? Shouldn't it be 27 and 57?

Thank you in advance.

 

[Mogman]

The "jumper" is the harness that goes from the contacts in the windshield to the wiper motor.
Sounds like solid troubleshooting, if the motor body is grounded and there is 24V on 27 then it should run.
Does 71 stay open (read high ohms) to ground as you put the wiper switch in different positions?

 

[MarkM]

Which wire are you calling #27? On the schematic the top wire is ground. The second wire down is power. The third wire down is to send power to the washer pump. The ground ring wire goes to one of the mounting lugs for the assembly. If you are bench testing the unit, use a meter to determine which wire is the power wire.

Put the switch on high and using the meter check the 3 connectors for a resistance load (going through the motor) between two of the wires. Now put the switch to off.

While pressing the washer button put one lead on the wire that did not have any continuity on the last test to one of the two that did have continuity. Once you complete the above tests you will now know the ground, power and washer connections.

Mark

 

[FlameRed]

Thank you both for your help.

I did a bit more testing and now see a difference between the old and new motor. On the old motor, #27 to ground stays infitite with the switch off. On the new motor the reading is 5.5 ohms with the switch off!?!?!?! I would have expected it to be infinite resistance with the switch off. I am not quite sure why there is not infinite on #27 to ground in the off position. Perhaps the new switch is defective, and the old motor defective?

I should have stated that the new motor has a new switch too, so different switches on both motors and they behave the same.

So #71 is for the washer. And I think that if you press the washer on, the power also should go to move the motor too.

Another test:

Infinite resistance between #71 (washer) and #27 (motor) when not pressing the washer button.
0 ohms between #71 (washer) and #27 (motor) when pressing the washer button.

If the motor body is grounded and there is 24V on 27 then it should run.

That is what I would have thought also. Neither motor runs with 24V on #27, and ground to the lug on the outside (paint removed) direct to the batteries.

Does 71 stay open (read high ohms) to ground as you put the wiper switch in different positions?

Correct 71 to ground stays infinite on all positions. When washer switch is pushed, it goes to 5.8 ohms. As I would have expected since I think that triggers power to motor.

On the schematic the top wire is ground. The second wire down is power. The third wire down is to send power to the washer pump. The ground ring wire goes to one of the mounting lugs for the assembly. If you are bench testing the unit, use a meter to determine which wire is the power wire.

I agree, that is how I read that drawing.

Put the switch on high and using the meter check the 3 connectors for a resistance load (going through the motor) between two of the wires. Now put the switch to off.

With switch on high:
#71 reads infinite (open) as I would expect for the Washer lead, unless pressed.
#27 goes to 5.5 ohms with the switch on high
#27 goes to 5.7 ohms with the switch on low.
What perplexes me is that on the new unit #27 to ground stays on 5.5 ohms with the switch off! ?!?!?! I would have expected it to be infinite resistance with the switch off. I am not quite sure why there is not infinite on #27 to ground in the off position. The old motor reads infinite with the switch off.

While pressing the washer button put one lead on the wire that did not have any continuity on the last test to one of the two that did have continuity. Once you complete the above tests you will now know the ground, power and washer connections.

 

[FlameRed]

I am wondering if I both the new and the old one are both defective!

I did some more tests. From the switch, there is a four wire connector that goes to the motors. I pulled the connector off the motor end on each, and measured the resistance from each lead to ground. There is a difference for when the button is pushed for the washer between old and new.

Makes me wonder if either the old or new switch might be miswired?!?!?! Makes me wonder since the old switch has infinite resistance between 27 and ground when the switch is off but the new switch has almost 0 ohms on 27 and ground when the switch is off.



Since it is pretty easy, I think what I will do it just connect the new switch on the old motor and visa-versa and see what happens.

EDIT: When I swapped the connectors from the switches at the motor and crossed them between units, now both units have a very small resistance from #27 to ground! Weird!

I might try putting voltage directly to the motor leads. On the connector to the motor, the four leads are labeled H, I, P and B. Not shown on the diagrams in the tech manual.

 

[FlameRed]

Ok, I have been staring at this for hours, and reran the resistance multiple times. I think the leads going into the wiper motor are as follows:

• H - high speed +24V
• L - Low speed +24
• P - Unknown - seems always to be infinite to ground, leads #27 & #71 on all switch positions on both units? Does not make sense.
• B - Battery? +24V

When you press the washer, you get connectivity from Lead B to 71 on both.

The only difference I see from all these tests is that on the new unit, lead L connects to #71, while on the old unit lead H connects to #71. So I assume on the new unit when you press the washer, you get low speed while on the old one you get high speed? Of course, I get nothing!

I am still pondering why with the switches connected to the motors, on the new one #27 to ground stays on 5.5 ohms with the switch off! ?!?!?! I would have expected it to be infinite resistance with the switch off. I am not quite sure why there is not infinite on #27 to ground in the off position. The old motor reads infinite with the switch off.

 

[MarkM]

The ground connection spade should be a direct connection to the shell of the assembly and when using the ground line to the mounting bolt the assembly is now grounded to the truck. Knowing the connectors put 24v to the power connector and the ground wire to the new battery. The unit should power up with the switch. See that it does on the bench before installing.

Mark

 

[Dieselmeister]

P - Unknown - seems always to be infinite to ground, leads #27 & #71 on all switch positions on both units? Does not make sense.

P is the power for the park position (In this case provided through the 27 wire). If you turn off the wiper in the middle of the cycle, this will supply power to the motor until it is in the park position, and then an internal contact opens the circuit.


I am still pondering why with the switches connected to the motors, on the new one #27 to ground stays on 5.5 ohms with the switch off! ?!?!?! I would have expected it to be infinite resistance with the switch off. I am not quite sure why there is not infinite on #27 to ground in the off position. The old motor reads infinite with the switch off.

Could be that the motor is not in the park position, and the contact in the motor is still connected.

 

[FlameRed]

Folks - thank you all for the help on this.

As sometimes for me, this turned out to be a comedy of errors that was not so funny. Turns out the positive red wire going to the battery directly I was using was defective, invisibly fraid, and although the VOM read 24V, there was just one strand of wire carrying the load. So that is why both the old and new motors appeared like they did not work.

Both the old and new motors work just fine. So I slaped the old motor back in, replacing the bushing and the clip. Now I have a wiper motor to sell I guess. This is what happens when I throw expensive parts at repairs.

Again, the wisdom of this board told me the most likely cause of my problem. I should have really paid attention.
I ran new wires to the motor as it appears that even though the old wires pass with my VOM, they cannot drive the motor. I assume it is the connector at the bottom of the windshield as pointed out by other members and that youtube. But with my helmet top that I don't have the means to remove, I could not get to it so rewiring seems more appealing to me.

I ran the wire #71 to the washer motor directly but the washer does not squirt or make any noise. I assume the washer motor was replaced somewhere along the line as it has a date stamp of 2015. No, I won't through parts at it! I'll figure it out.

So again - thanks to everyone that helped me!