Author Topic: Hardtop rear window defroster  (Read 3414 times)

TEJOLX47

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Hardtop rear window defroster
« on: April 12, 2016, 10:07:21 »
Hi everyone,

I have bought a 1970 280SL and I am in the process of a step-by-step improvement.
My Pagoda was originally delivered to the USA with tinted windows and rear defroster.
I can verify that through the existence of a cabling harness on the hardtop, the cabling plug on the chassis (right behind the driver) and a cut on the centre console to acommodate the switch.

However, the current window does not have any defroster resistance, and I miss the switch in the console.
Has anyone had this proble? Do you know how to solve it?
Where to buy the parts?
Basically I need the resistance, probably a new harness and new switch.
Many thanks
Francisco
Francisco

1970 280 SL (US delivered, Auto, AC, PS)
181 Light beige with 423 Tobbaco brown top

mmizesko

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Re: Hardtop rear window defroster
« Reply #1 on: April 12, 2016, 13:31:56 »
The switch and mount for the center console tray is sometimes available on ebay.  As for the wiring, You'll need to find out how much is still intact.  As for a short in your defroster wiring inside the glass, It may be in the pigtail harness, or could be in the glass itself, where you may not have any recourse.

Mike Mizesko
Columbus, OH
1970 280SL 291H Dark Olive

chumps

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Re: Hardtop rear window defroster
« Reply #2 on: April 12, 2016, 15:02:23 »
I have the center pull switch, the wiring to the rear, the harness plug and the hard top wiring in place. Is there an easy way to determine if the rear window  is in fact a heated window or a replacement that is not heated? I live in warm sunny So. California so I have never had a need to use it. I can not see any resistence wiring inside the glass with the naked eye. Thank you.

TEJOLX47

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Re: Hardtop rear window defroster
« Reply #3 on: April 12, 2016, 15:48:35 »
Good point.
I cannot see any wiring inside the glass, and that led me to believe it had been replaced.
But I'm not sure...

Francisco
Francisco

1970 280 SL (US delivered, Auto, AC, PS)
181 Light beige with 423 Tobbaco brown top

TEJOLX47

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Re: Hardtop rear window defroster
« Reply #4 on: April 12, 2016, 15:50:41 »
Thanks Mike!
Francisco

1970 280 SL (US delivered, Auto, AC, PS)
181 Light beige with 423 Tobbaco brown top

Tyler S

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Re: Hardtop rear window defroster
« Reply #5 on: April 12, 2016, 16:00:19 »
The resistance wires in the rear glass are very tiny. They are not obvious like modern cars. You almost need a magnifying glass to see them. They are as thick as a strand of hair. In a zig zag pattern.
You can test to see if they in fact exist and are hooked up by checking the resistance with an ohm meter at the electrical connector on the hard top. If your meter shows infinate resistance they dont exist, are damaged, or are not hooked up. A working resistance grid should have about 2 ohms resistance.
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TEJOLX47

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Re: Hardtop rear window defroster
« Reply #6 on: April 12, 2016, 16:12:56 »
Many thanks Tyler.
That seems to be the right way to check if they are there.
If not, I guess finding glasses with resistance won't be easy.
Cheers
francisco
Francisco

1970 280 SL (US delivered, Auto, AC, PS)
181 Light beige with 423 Tobbaco brown top

TEJOLX47

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Re: Hardtop rear window defroster
« Reply #7 on: April 12, 2016, 19:27:42 »
After a little detective work - magnifier and lamp included - I found the resistance.
Tiny. Almost invisible.
I will test the resistance in the weekend to check wether it's still working.
Thank you very much for all the help.
Cheers
Francisco
Francisco

1970 280 SL (US delivered, Auto, AC, PS)
181 Light beige with 423 Tobbaco brown top

mmizesko

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Re: Hardtop rear window defroster
« Reply #8 on: April 12, 2016, 19:48:05 »
All you need to do to see the grid in the glass is hold a sheet of white paper up against the inside of the glass, and use a flashlight.  It will be obvious.

Mike Mizesko
1970 280SL 291H Dark Olive

chumps

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Re: Hardtop rear window defroster
« Reply #9 on: April 12, 2016, 23:00:45 »
Thanks for the information. I will check this evening. Chumps