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1973 450SL
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Discussion Starter #1
I have been working on electrical problems on my recently acquired 1973 SL and ran across disconnect/ cut wires and connectors. One is frm the defroster switch. The wiring diagram shows 4 wires going to the switch but physically there are 5 wires. One being independent from the harness and in my case, it is cut. Does anyone know what it is and where it goes?
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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That is a fiber optic line. I don't know where the light source bulb is on a '75. Here is a pic of the bulb and connector in a '78 with link to location of bulb and connector in a 380SL.
 

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1973 450 SL
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That fiber optic line lights up the defroster switch. The other end of it was connected to a brass light distributor on the bulb that illuminates the top of your right side climate control slider legend. My car had another light distributor on the left side to illuminate the cruise control switch legend. I have added an antenna switch which also uses fiber optic lighting.

I struggled with these things for years because they had been bent and twisted; would not stay in place. I collected a light distributor from a later model, mounted it on the dash support between my radio and glove box and installed an LED bulb in the light socket to improve that passive lighting. These pictures were taken using a bulb that was too white. I have since changed the LED to a softer yellow - pleased with the results.

Fiber Optic Distributor (2).JPG

Fiber Optic Distributor (4).JPG
Fiber Optic Distributor (5).JPG
Fiber Optic Distributor (6).JPG
Fiber Optic Distributor (7).JPG
Fiber Optic Distributor (12).JPG
Fiber Optic Distributor (13).JPG
 

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1973 450SL
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Discussion Starter #4
Thank you, at least I now I know that it will not have any impact for not having it connected. I do not see fiber optics anywhere on my car. Maybe the 73 did not have it?!?! And this switch was “borrowed” from a later model?!?!
 

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1973 450 SL
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Fiber optic lighting was installed in your car. The black line in the first picture of post #1 is a fiber optic line. That line can be pulled out of its socket. Take it out, point it at a light bulb and look at the other end and you will see how it works. I like the feature and chose to improve on it because the light distributors described above were difficult to keep in position. Your rear window defrost switch is not borrowed. It was installed with passive fiber optic lighting so you can see it at night.
 

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Premium Member
1983 380SL, 2000 S430, 1991 420SEL (retired) - RHD
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Can I ask a stupid question please. What is the large silver box with an MB part number on it. The radio?

The reason I ask is that the large pelican shaped hook is present in my car but not connected to anything as shown in your pics. ❓
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Can I ask a stupid question please. What is the large silver box with an MB part number on it. The radio?

The reason I ask is that the large pelican shaped hook is present in my car but not connected to anything as shown in your pics. ❓
It is indeed the radio. Do you have a stock radio in yours?
 

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1973 450SL
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Discussion Starter #8
Fiber optic lighting was installed in your car. The black line in the first picture of post #1 is a fiber optic line. That line can be pulled out of its socket. Take it out, point it at a light bulb and look at the other end and you will see how it works. I like the feature and chose to improve on it because the light distributors described above were difficult to keep in position. Your rear window defrost switch is not borrowed. It was installed with passive fiber optic lighting so you can see it at night.
I believe my car was heavily modified electrically by the previous owner(s) in that particular area, hence the cut fiber optics cable on the defroster switch and no other fiber optics remanence. I would really like to bring it back to as close as possible to original as I can but I don’t have and can’t find any “fiber optics diagram” or pictures from that area that shows how it should be connected. Does anyone with an early SL have pictures that would help me piece back together the original lighting behind the console?!? It would be really appreciated.
 

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1973 450 SL
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Here are some pictures of the two lights at the top of the climate controls in the console. The problem I had was mounting these in a replacement (1980 model) console. I could not get them to stay put and they tend to chew up the console material. Focus on the metal pieces on these lights. The little tabs on the inner console side accepted another clip piece that held the fiber optic line in a position to stare at the bulbs.

Mercedes improved this setup. Member @okyoureabeast posted some pictures of his inner dash that prompted me to solve the problem. I went to the salvage yard and pulled parts from several sedans to build what I posted above. I appreciate originality but it was not possible in this instance because my original console was trashed.

IMG_3064.JPG
IMG_3065.JPG
 

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1973 450SL
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Discussion Starter #10
Thank you, I am having trouble finding parts to replace the fiber optic cable and even if I do I am not too sure of the efficiency. I am likely going to substitute the fiber optic cable with an miniature LED that fits on the switch socket where the fiber optic cable goes. I was just looking at the back of the ac switch panel and realized that the defroster indicator should have a light behind it but it is empty. Do you know where this light should be connected and when it should come on?
 

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Because of this thread, I was playing with that switch yesterday. I had a multimeter in the plug for the rear window defrost. I have not activated that switch in years because my hard top is in storage. It appears the switch has an integral light that illuminates when the switch is activated and stays illuminated as long as the timer relay for the rear window defrost is closed. The fiber optic light is only for illumination of the "fish in a pan" legend on the switch.

The other interesting thing . . . could not find this circuit on the 1973 wiring diagram.
 
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