Need assistance with Mk4 rear wiper circuit

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Rembrant

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Hi Folks,

Is there anybody here with intimate knowledge of the Mk4 rear wiper circuit?

I'm having an issue with mine that seems strange, and I can't quite figure it out.
I think the only thing left that I have not done is bench test the rear wiper motor (Which is a brand new aftermarket unit).

It is a bit of a long story, but I'll give you the current details to see if it makes any sense:

When I switch the rear wiper to ON, it works as it should, but when I switch it off it keeps on running (normally) forever.
If I pull back on the switch to activate the front wiper wash, the rear wiper will stop.
This made it seem like a bad switch/stalk, so I swapped it with another one, and the same problem.
I completely removed the switch/stalk from the steering column, and the problem is still there with the contacts jumped.

If I jump ground to wire #97, it gives the rear wiper board the input to run. Remove jumper, and the wiper motor stays latched on.
The only way to stop it is to switch 12vdc+ on to wire #97, or turn the ignition off.

The only other thing that wire #97 touches is the J31/377 wiper relay, so I removed it too.

Now, with the front wiper relay removed, the rear wiper will start and run as normal, but when you open the contact to stop it, the wiper motor goes into the rear wash cycle before it stops. It did it 3 out of 4 times I tested it.

Does that sound like the rear wiper motor/board is faulty? It is brand new, but it could still be bad.
If not, does anybody have any tips on what else I could check?

I replaced the wires/grommet between the body and hatch two years ago, so I assume they are OK, but I have not checked them since.

Any suggestions at all would be appreciated.

Thanks,
Rem
 
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Rembrant

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Ok, maybe I can simplify my question(s)...

I can't find any help in my Bentley manual.

If I switch my rear wiper on, even just for a second, it latches on.

If I remove the #377 wiper relay (J31) it does not do this. Does anybody know why this relay would cause the rear wiper circuit to latch on? It is not a problem with the relay itself...I have changed it and the problem is still present.
 
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PetrolDave

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Sounds like the switch that detects the wiper has reached the park position isn't operating correctly.
 
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MartinsX

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Recheck wiring where wires go from tailgate to roof ;)
 
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Rembrant

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Sounds like the switch that detects the wiper has reached the park position isn't operating correctly.
I did bench test the rear wiper motor and it works just fine when removed from the car.

I've been playing around with it some more, and I think the issue is with the input(s) on the new rear wiper motor/control board. The wire for the rear wiper "on" has a constant 1.2 k Ohm to ground because of the front wiper relay (377). This new aftermarket wiper motor/board I bought must have inputs that are sensitive enough that the 1.2 k ohm to ground will keep the input ON after it has been activated. I assume the inputs on the original OEM motor/board were not this sensitive and actually required a full 12v negative input to stay on.

I'm just theorizing here...I'm not an electronic guy. I can handle relay logic, but circuit boards are not my thing.

I think I'm just going to add an interposing relay on this input line for now (to isolate the 1.2 k ohm to ground from the 377 front relay). I hate to "fix" it that way, but I don't want to spend $300 bucks on an OEM VW motor/board when I'm not 100% sure that is the problem. I'm just guessing right now.
 
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Rembrant

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Recheck wiring where wires go from tailgate to roof ;)
Hi Martin,

I currently have two new left and right harnesses on order from the VW dealer. For now, I have both harnesses routed directly in the car's interior, and the wires really do look fine. The wires on the right hand side were cracked/broken, but they are not for the wiper circuit. I have repaired them temporarily.
 
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MartinsX

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Is Your washer pump connected and in working order?
 
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Rembrant

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Is Your washer pump connected and in working order?
Yes, it is connected and working OK. I did try unplugging it, and I swapped another one in as well, and all the same.
 
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Rembrant

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Ok, my clever idea of using an interposing relay is not going to work (for a couple reasons). Oh well...

Anybody have any ideas or suggestions on things to try?
 
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