I just pulled out the rear wiper assembly on my 300DT 1983 wagon. Have not fully diagnosed the problem, but here is what I found so far:

• The rear wiper switch seems to be working. I measured 12V between pins 3 and ground at the rear wiper.
• Motor does not turn. Upon opening the gear box assembly thingy, I noticed the main plastic gear (white with lots of brown grease on it) has copper terminals with shapes cut in - I suppose this is to reverse the motor direction as the gear turns.
• Voltage to the gear is supplied by three terminals that are fed by wires on the outside of the assembly housing.

I wanted to know if anyone else has attempted with fix before and knows what to do here?

Talk with "Shawn D".
Here is his thread.

I've Just About Had It! (LONG, RANT)
I've Just About Had It! (LONG, RANT)







Have a great day.

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The problem with my 300td's wiper assembly was physical destruction of linkages and the aluminum casting due to multiple screws backing out. Thankfully, I was able to cobble together a good one after obtaining another damaged one from a junkyard car.

I'd continue disassembly until you find what's binding the motor. Maybe there's a loose screw jamming the works. I still have some parts in the corner of the garage, so if you find something that's broken, maybe it's OK on what I have left.

make up some jumper wires and see if you can make the motor run by jumping direct to the battery. If it runs that way, then just clean all that out hardened grease, re-lube, an re-install it. Then start looking for the wire that is shorted out and you can just about bet it'll be around the hinge area of the rear hatch.

Turn on the switch and start jiggling the wire bundles. Pretty simple, but still a PITA! Frankly, I did all the above about 18 times, tried 2 other used motors, cleaned switches, replaced the 58 buck relay, and nothing worked until I jiggled that bundle of wires....found the short and re-spliced it.

I had forgotten about the "backed out screws"...mine had the same deal and you'll see what we're talking about if your's are the same way. I also resorted to zip ties to re-attach the black plastic cover that had deformed over 25 years. Zip ties are a good thing!

Rainy days, it sure is nice to have a working rear wiper.

__________________
Mark
1983 300TD Wagon
Even a broken watch is right twice a day

When I saw the thread title I knew you would have an informative post on here! Man do I remember you battling with that wiper issue....

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2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

I have also had screws back out and cause failure of mine. Turns out the brushes on the motor commutator had burned enough to cause a short (screws caused motor to be unable to turn). Once I sanded off the deposits the motor worked fine. Might be worth a shot.
bb

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My thought was; these folks might have what you need in their mass of rear wiper spare parts.

Cool...thanks folks. I am going to work on it now and let you know what I find in the morning.
Good night all!

The trim pieces on the rear tail gate of my 300TD wagon are deteriorating. Anyone of you guys willing to sell me some replcement trim pieces that can fix while I am working on the wiper motor?

I managed to fix the motor, but frustratingly enough...when I connected it back up again, I could not measure any voltage coming from the connector with the switch in the ON position (I could have sworn I saw 12V on it yesterday).
So now I am thinking about broken wires?, relay?, switch?
Can someone tell me where the relay for the rear wipers is located and how to access it?...I plan to start there and work my way down.
Thanks!

That relay is about 60 bucks and I bet it is still good. It is located behind that pillar on the hatch...outta sight, you gotta do a reach around to get it...small box 1" square x 2" long, pull it straight out, it has pins sticking outta the bottom.

I'm still betting it is a short...trace those wires up towards the top of the hatch and start looking where they come out of the hatch and back into the roof of the wagon. It's right there in front of you, just look up. Sorry I can't remember what color wire did what and No way am I gonna tear into that hatch AGAIN!!

__________________
Mark
1983 300TD Wagon
Even a broken watch is right twice a day

Yep,
Relay is gone. Dont know where it went..but I located the receptacle inside the hatch (on the passenger side of the hatch). Fished around a little bit to see if the relay had fallen off..but it was not there.
Anyone have a spare relay they can sell me?
If not, please let me know what the part number is.
Thanks!