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  #1  
Old 03-29-2017, 11:56 PM
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Rear windows blow fuse when operated from front switch

Hi guys I am new to the forum and have a big issue with my 84 300D Turbo. What going on is that I can roll down my rear windows using my rear switches and I can roll down my front windows using my front switches, however when I try to roll down either rear window using the front switch my fuse blows for that window.

To date I have done the following- replaced the relay, replaced the master driver switch with an old one (not sure if it works), removed the door panels and verified that the two wires at each window that should have 12.6v indeed do. I have pulled out the carpet and traced all wires looking for a short. I have even jumpered each window right to the switches. All that and no change.

I am becoming very desperate and have even ordered a new master switch and expect it to arrive later in the week. Any help or ideas is greatly appreciated.

Daryl
Decatur, AL

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  #2  
Old 03-30-2017, 02:34 AM
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In a W124 it means wires in the flexible loom across the door hinge have failed insulation.

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98 E320 wagon
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Old 03-30-2017, 09:48 AM
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It's not the wires in the door as I have jumpers all those to eliminate that cause.
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Old 03-30-2017, 11:27 AM
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I agree with Sixto its a bad wire in the B pillar - written HERE many times.
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Old 03-30-2017, 11:58 AM
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Did you just "jumper" the wires or jumper AND DISCONNECT the wires?
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Old 03-30-2017, 07:19 PM
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I disconnected every wire that can go through a pillar and snipped the corresponding wires off at the switches and spliced new wire in. Yes I am that desperate. However, That did not fix it. I am lost at this point and need help on what to try next. The new driver door switch just arrived and it did not repair the issue.
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  #7  
Old 03-30-2017, 08:05 PM
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Quote:
Originally Posted by dsp123 View Post
I disconnected every wire that can go through a pillar and snipped the corresponding wires off at the switches and spliced new wire in. Yes I am that desperate. However, That did not fix it. I am lost at this point and need help on what to try next. The new driver door switch just arrived and it did not repair the issue.
This is bit of a stretch, but I once had a similar issue and the cause was a bad switch. IIRC, (wish I had the circuit diagram handy), the power passes through one switch on the way to the other. I found that out when pulling one of the switches caused the window to not work at all, even from the one that was still connected. I forget which way around that was... But there are two rockers in those switches, and two little ball bearings. The plastic tubes that are part of the switch button hold springs and two ball bearings. Sometimes the plastic tube breaks and the spring and bearing escapes, and that can cause all sorts of weird issues. I would swap switches left to right on both the console switches and the door, and see if the problem follows.
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Old 03-30-2017, 09:33 PM
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Attached are the window wiring diagrams. At this point I am at a loss, I have the dash out the seats and carpet out, I have pulled and traced very wire I can find. Out of desperation today I have decided to go ahead and order a passenger side switch just to rule that out and to order one rear switch as I already have one spare for it.

Im at a loss as of what to try.
Attached Thumbnails
Rear windows blow fuse when operated from front switch-123-window-elec-1-2.jpg   Rear windows blow fuse when operated from front switch-123-window-elec-2.jpg  
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  #9  
Old 03-31-2017, 10:47 AM
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Another thing to check is that the proper amperage fuse is being used. And check the amperage draw of the window motor with an amp meter.
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  #10  
Old 03-31-2017, 05:23 PM
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I will look over these annoyingly German schematics tonight and see if I can find a commonality.

To be clear - you ONLY have this problem when rolling DOWN the rear windows via the FRONT switches? It's ONLY the rear windows, and ONLY when going DOWN correct? You do not have this problem when rolling UP either window with either switch?
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1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition
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  #11  
Old 03-31-2017, 07:26 PM
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Ok, I think I have a working theory. I think you have a bad switch, but not one of the ones you'd expect. There is a weird shared ground setup here and the circuit reverses polarity depending on window direction (up or down), and if one of the switches is failing to disengage from either leg, it could make a dead short.

The power also passes through the front switches on its way to the back windows. If you remove the front switch for the rear window, the rear window will not work at all. When you use one of the front switches, you pass power to the rear motor on one wire and provide ground to it from the other. The polarity of this changes depending on if you are rolling up or down. One switch failing to disengage fully could be causing this.

Here's a test I propose. Start by disconnecting center console switches. Disconnect all but the switch for the driver's rear window. If the fuse still blows, disconnect all but the switch for the passenger rear window and try again. If you wind up with it working in one of these scenarios, re-connect each of the center console switches one at a time until the problem re-appears. That will be your defective switch.
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1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition
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  #12  
Old 04-01-2017, 10:09 PM
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I will try this and let you know
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  #13  
Old 04-01-2017, 11:07 PM
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The fuse blows when you try to roll the rear window up or down using the front switches
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  #14  
Old 04-02-2017, 02:07 PM
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The problem is the switch on the center console. Remove the switch and swap it with another switch on the console, preferably on the other rear window switch and it will then cause that fuse to blow. Get a new switch.
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  #15  
Old 04-02-2017, 09:16 PM
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I already replaced the drivers master switch and that did not repair the issue. I have ordered a new passenger front switch and 1 new rear switch. Those will be in later in the week. I did try one of the old drivers switches in place of the passenger master switch and that did not fix the issue. I am hopeful one of the new switches will take care of the issue.

Daryl

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