Mercedes-Benz Forum banner

Rear windows blow fuse when operated from front switches

4K views 21 replies 5 participants last post by  dsp123 
#1 ·
I am posting this again because I am desperate and looking for help. Below is what I have tried to date.

So today I went out and pulled all door panels, all seats and carpet and started tracing. One interesting thing happened when I would open and slowly close the driver rear door the lights on the seat switches would illuminate. When I saw this I immediately thought I had found the problem so I fished new wire through the door and attached it at the point where the wire starts coming up the B pillar however, there was no change. So next I assumed the short was further up the line so I then I the wires all the way up to the switch harness to see if that would cure the issue and again no change. So next I moved onto the drivers door and thought I saw what was a chaffed wire where the wire moves through the doors so I once again fished another new set of wires through the door and wired them up and no change. I then moved to the passenger side where I saw no issues with the wires passing through the doors. I then started cleaning grounds, I cleaned the one in the gearcase, one under the hood near the passenger side front turn signal and the two behind the cluster. I then changed all fuses as instructed by other members on other post with these issues and then I tried my spare switches........NO CHANGE........The fuses still blow when you try to operate the rear windows with the center console controls. They continue to operate perfectly when controlled by the rear switches. They also are still not illuminated.

I am getting desperate here guys......could it be the relay? Does anyone know where the ground for the windows attaches?

Any and all help greatly appreciated at this point.
 
See less See more
#3 ·
I had a similar problem with console switches, the one for the right rear window blew the fuse. The right side switch was extremely worn out, (the buttons, springs, balls and the metal plate that makes the contact, all shot). In my case, it didn’t matter if you activated the switch or not, as soon ignition was on, the fuse blew. I replaced the switch and no more problem.

You said you tried a spare switch, is it new or used?
 
#4 ·
Yes, I replaced all switches with new ones out of frustration and that is actually the second new driver's side switch since I took ownership of the car. I kept all switches and have tried old and new and everything. Do you know if there is a way to test a switch with a multimeter to see if it is shorted out? Again, both rear windows blow the fuse only when using the front switches. I even unplugged the driver's side switch and got the same result and again with the passenger rear window and the same with the passenger side switch. If it is a wire that is causing the issue it has to be one that is shared by both rear windows. I am simply at a loss as what to try next.
 
#5 ·
Brown is ground, black is not if that helps.

Relay is behind instrument cluster which requires removal of. Careful with the oil pressure line or you'll have a new headache.

When you look back there, the big black one to the left side is for the rear defroster. The one to the right of that is the wiper relay. Now you'll see the 2 little ones to the right of that, those are the window relays.

Helluva place to put them huh? The only thing I can conclude for their inconvenient location is to keep the power run as short as possible to fuse box because of the amps they pull and the need to keep them from ever getting wet by placing them high and inside.
 
#8 ·
I was able to get these drawings however I am not good at reading them. All I know is I have continuity between the wires at the main center console switch and all the windows, I went out and reverified that today. I also know that I have no illumination on any of the switches and it used to be sporadic before this issue so I am assuming it is tied in there somewhere.
 
#10 ·
Take a look at this document:

https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/ETM/82_300_howto.pdf

It says how to read the diagrams. It specifies symbols, wire colors, connector terminal number and even wire sizes. That will help you a lot. The diagrams are hard to read and they are cut since they don’t fit in just one page. Take both halves of the diagram and put them side by side, so you can a complete image of the circuit.

Full electrical diagram in PDF (HQ):

https://www.startekinfo.com/StarTek/outside/12265/disc_2/program/ETM/82_300.pdf

Take your time and study the diagram. After a while, you will understand how the components are wired.

I am not an expert, but according to the diagrams (shematic #124), the illumination wires (center console) are blue, grounds are brown.
The connector for the switch illumination is #6 in and the ground is connector #4 (and #5 for the safety switch on the left one).

The wires for the power windows (wires to the switches and from the switches to the motors, schematic #132) are red/black, red/white, green, red/yellow, green/black, red, black/white, blue/white, pink/red, black, brown (ground)

Also, this has me thinking,

One interesting thing happened when I would open and slowly close the driver rear door the lights on the seat switches would illuminate.
Does the problem also occur when the doors are open or being closed or opened?,

When the windows go up or down, or both?

With the lights on or off?

Did the car had the problem when you bought it?
 
#11 ·
Thank you for those documents, i will definitely study them.

To answer your questions....The car did not have the issue when I inherited it from my grandfather, it suddenly started one day and began as an intermittent issue but has since developed into a full time issue.

It happens regardless of the windows going up or down.

Lights on or off? Good question and I'm not sure. I would go try it with the lights on but I have the instrument cluster pulled and sent off to Specmo to have the odometer gears and some circuits on the PCB board repaired. Can the light switch cause the issue?

Brief history on the car- my grandfather bought the car new in 84 and was his daily driver. He raised me and it was the car I learned to drive in. The car was always garage kept until his later years when he sold his home and moved to a retirement home. At that point the car stayed outside in the elements full time and developed the usual leaks. I have been working hard to return it to its old glory and plant to have it repainted and new carpet and upholstery for my daughter to use as her daily driver to college. She loves the car and is very exited about the restoration process. I have done several projects such as rebuild the blower motor, complete suspension/gearbox overhaul, wheel bearings and the usual oil leaks. I thought a lot of those were tough until I tackled this window issue.
 
#13 ·
Can the light switch cause the issue?
Not sure. I thought about because in post #8, you said that maybe the lack of illumination on the switches had something to do with the problem.

I have ordered a new drivers front switch just to rule things out.
The probability of having 3 bad switches in a row must be very close to 0.

Considering that replacing the switches, relay and fuses and cleaning the grounds didn’t have any effect, it must be a wiring problem caused by a broken, fractured or deteriorated wire or its insulation, or a loose/damaged connector somewhere on the power windows circuit.

Generally, the wiring breaks or fractures between the door and the doorpost because of opening and closing the doors. Also could be damaged due to improper handling (caused by someone in the past before you got the car) like lifting the center console too high while replacing a switch, applying excessive force while disconnecting an electrical device or while reinstalling something (a wire can get jammed between two parts and fracture). That sort of damage may show immediately or may show up latter as the wiring and its insulation or any repair done to it deteriorates.

You will have to check very carefully for damage on the wiring, loose connectors, missing wires or anything that doesn’t look stock. Just don’t forget to disconnect the battery before doing any diagnosis.

And, since you removed several parts of the interior, lube the window regulators and clean the drains at the bottom of the doors.
 
#15 ·
I have been studying the diagram and I went out today and verified that each door had 12.6v on the two wires that should at each door. No issue there. My question is....how do I check the grounds? Still waiting on the new switch but what if it is the passenger switch or one of the rear switches? Is there a way to test the switches with a multimeter?

Please help
 
#19 ·
If I understand the issue, The fuses (2) blow if the rear windows are operated from the front console switches. And both rear window switches work fine from their rear doors. If that's correct you have a short in the harness from the console thru each door pillar or at a door sill harness as it passes to the rear of the interior. A short is a bare wire touching metal before it reaches the switch. So... I would look at both wire harnesses where they pass thru the center pillars (B pillars) between the door hinges, or under the carpet below the door sills. A broken wire is an open circuit which doesn't blow a fuse. Pull off the door sill moldings and pull the wires out of the plastic conduit looking for a pinched wire along the harnesses length on both sides.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top