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  #1  
Old 03-11-2008, 07:31 PM
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Join Date: Feb 2008
Posts: 96
rear window defroster, W115

Hi,

I have a 1971 220D with rear window defroster, which does not work. I have voltage on driver's side up the the wire on the panel behind the rear seat. The ground wire on the passenger side is also intact. I can follow these wires through the panel into the trunk, then they snake up around the mounting for the trunk hinges. I can only feel (not see) and they seem to go through the sheet metal. How do they connect to the element on the window? The heating element is intact and painted on the inside surface of the rear window, not between glass surfaces. Inside the car, on the window, the horizontal element stripes end in a vertical bar which goes under the weather strip. How is the connection made to the wires in the trunk? Should I pull away the weather strip inside? Or outside? Inside, I pulled the weather strip back a little bit, and can see only the headliner, which I'd rather not mess with.

'Sorry if this has been covered before, I looked and couldn't find reference to pre '74 cars.

Any suggestions would be helpful,

Ron

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1971 220D, daily driver, new paint, 142K
1973 220D, low compression
1975 300D, back on the road! 166K
1971 220D, salvage, rear hit, engine excellent
1972 250, bad cam, but runs!
1971 230, engine stuck
1971 220D, low compression, rusty
1976 240D, salvage, engine excellent
1966 230SL, water in oil after rebuild
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  #2  
Old 03-11-2008, 08:06 PM
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Join Date: Nov 2006
Location: A constant state of confusion.
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I'll be watching this because I have a similar problem. From what I understand (and I'm coming from a poorly researched point of view) the wiring between the window and the fuse box can be totally fine like mine and it may still not work as the silk-screened lines become more resistant to the flow of electricity as they get older. Mine used to work reasonably well and now barely at all.

I was hoping some local vandals would shoot it out and have my insurance cover a new one. True story, they figured if they shot out older car windows the cost would be lower if they got caught. I hope there's an easy solution or that your problem doesn't suck as much as mine. Good luck.
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  #3  
Old 03-12-2008, 09:08 AM
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Location: Tucson, AZ
Posts: 5,358
Double-check the ground. Remove it, CLEAN the connection and re-attach. Ohm test it. I've had a few of these which looked fine but the wire itself had become brittle at the crimped portion on the connector.
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  #4  
Old 03-12-2008, 10:49 AM
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Join Date: Feb 2008
Posts: 96
Ok, I'll do that this weekend Mike. I'm assuming it is the connection behind the rear seat back. I still do not know how to access any connection between the glass's heating element and the wire that is passing through the trunk. In other threads it seems that in the 123 chassis, it is the glass's element/wire connection that goes bad. Ron
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1971 220D, daily driver, new paint, 142K
1973 220D, low compression
1975 300D, back on the road! 166K
1971 220D, salvage, rear hit, engine excellent
1972 250, bad cam, but runs!
1971 230, engine stuck
1971 220D, low compression, rusty
1976 240D, salvage, engine excellent
1966 230SL, water in oil after rebuild
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  #5  
Old 03-12-2008, 01:08 PM
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Join Date: Jun 2005
Location: Chicagoland
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Quote:
Originally Posted by Zeppo2K2 View Post
I can only feel (not see) and they seem to go through the sheet metal. How do they connect to the element on the window? The heating element is intact and painted on the inside surface of the rear window, not between glass surfaces. Inside the car, on the window, the horizontal element stripes end in a vertical bar which goes under the weather strip. How is the connection made to the wires in the trunk?
I removed the back glass from my 1972 250C (w114) 3 months ago. There is a flat braid wire that runs on the edge of the glass from about 1/2 way down the glass to the corner. Notice that I said edge - it is neither on the outside nor the inside of the glass.

The gasket has one hole in each corner - the wires from the trunk come up, through the hole in the gasket, and are soldered to the flat braided wire.

Let me know if this doesn't make sense. I can take a picture of the glass if it will help.
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  #6  
Old 03-12-2008, 04:00 PM
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Join Date: Mar 2007
Location: Hampton Roads, Virginia
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Quote:
Originally Posted by thorsen View Post
I removed the back glass from my 1972 250C (w114) 3 months ago. There is a flat braid wire that runs on the edge of the glass from about 1/2 way down the glass to the corner. Notice that I said edge - it is neither on the outside nor the inside of the glass.

The gasket has one hole in each corner - the wires from the trunk come up, through the hole in the gasket, and are soldered to the flat braided wire.

Let me know if this doesn't make sense. I can take a picture of the glass if it will help.

Same setup on the sedan.

Window needs to be pulled to see the connection.

Test the continuity from feed wire to the vertical strip on window glass edge to verify a connection. Same on Pax side for ground.

Jim
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  #7  
Old 03-13-2008, 01:21 AM
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Thorsen and Jim, this makes a lot of sense and I can picture it now. I'll take the seat out this weekend, do the measurements as you say, and let you know what I find. (Too bad if solder connection in gasket is bad, I guess you have to remove the window.) Hopefully I find that ground wire is the problem as Mike suggested. Ron
__________________
1971 220D, daily driver, new paint, 142K
1973 220D, low compression
1975 300D, back on the road! 166K
1971 220D, salvage, rear hit, engine excellent
1972 250, bad cam, but runs!
1971 230, engine stuck
1971 220D, low compression, rusty
1976 240D, salvage, engine excellent
1966 230SL, water in oil after rebuild
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  #8  
Old 03-16-2008, 08:42 PM
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Join Date: Feb 2008
Posts: 96
Hi resistance in window conductors

OK, following the advice I received, I tracked both connections to the rear window. There's 12v on the passenger side, on the strip on the window. But as you move the meter probe towards the center of the car on one of the conductor elements, the 12v goes to 0 about 6 inches from the right edge of the window. The drop occurs for about 4 inches, then nothing. On the driver's side, there's ground on the strip on the window edge. Then as you move to the center on one of the elements, the resistance goes up, slowly at first, then in a few inches, it goes up to 10's of thousands of ohms.

This occurs for the 5 or so elements I checked. So it appears the center field of my window defroster is high resistance. I can see no breaks in the traces.

The only thing that comes to mind is buy some conductive paint and try to paint over the strips, several feet for 16 traces on the window.

Any ideas?

Ron

__________________
1971 220D, daily driver, new paint, 142K
1973 220D, low compression
1975 300D, back on the road! 166K
1971 220D, salvage, rear hit, engine excellent
1972 250, bad cam, but runs!
1971 230, engine stuck
1971 220D, low compression, rusty
1976 240D, salvage, engine excellent
1966 230SL, water in oil after rebuild
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