Author Topic: Mystery switch and dash lights  (Read 1867 times)

Reischmann

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Mystery switch and dash lights
« on: January 22, 2013, 13:05:30 »
When I removed the tach and center instrument cluster I found a momentary on switch (0343105008), attached to the factory harness, just sitting there.
Anybody know what it is and where it goes?
Also, the dash lights will not dim, using the dimmer control?
Thank you,
Mike
1970 280SL

w113dude

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Re: Mystery switch and dash lights
« Reply #1 on: January 22, 2013, 13:27:32 »
I have never seen any switches behind the cluster,  most likely this is the switch that was added to by-pass dimmer.
Shaun Pooladian

67 250SL Auto late, Euro under restoration
70 280SE Coupe factory 5speed
72 250C  (for sale)
80 300CD, converted to 4sp manual, every day driver

Reischmann

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Re: Mystery switch and dash lights
« Reply #2 on: January 22, 2013, 15:46:36 »
Thanks for the quick reply.
It is a spring loaded, normally open, micro switch.
It looks factory.
Did you see the picture attached to the original email?
Mike

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Re: Mystery switch and dash lights
« Reply #3 on: January 22, 2013, 16:18:06 »
What Shaun has already mentioned...

There _is_ no additional switch behind the cluster from factory. :o Yours is clearly an aftermarket and a shade-tree mechanic solution. 8)


It is very common that the dimmer rheostat for the dash light deteriorates when aged. This is especially true if it was not used in the past (dimming around to prevent corrosion).
As a solution a by-pass bridge is very common - as Shaun already said.

The rheostat is NLA and I do not know of a suitable replacement.
Maybe one of a /8 or even a W110 fits but I have not tried yet.


Achim
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pagoden

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Re: Mystery switch and dash lights
« Reply #4 on: January 23, 2013, 09:13:59 »
Mike, something doesn't make sense here.  Shaun and Achim are surely correct in concluding that the switch is an improvisation; beyond the fact that they both know their stuff, the part number is nowhere near an M-B number, much less one contemporary with our cars.  And plugging something in at that point would be a tidy bypass/shunt/jumper - - except that you seem certain that the switch is a normally-open momentary type, which couldn't possibly serve in that capacity.  So just to be clear: you've tested the switch and are certain of its function?  [If it were actually the opposite -- normally closed -- of course that would make it a workable fix, and I have seen some that were convertible though that one doesn't look like it.] 
Certainly is a puzzle as to why such a thing was chosen, and even more, how your dash lights could function at all with the circuit normally-open at that point.  Maybe it's a problem with terminology: electricity-speak for a switch that passes current through is to refer to it as closed, and an open anything -- switch or entire circuit -- will not allow current through because there is an open gap there, so no path for the current to follow.  It's like taking out a section of railroad track or blowing a bridge, not like shutting a valve.     
We have excellent circuit diagrams in our Tech Manual section which are accessible to full members.  [Most of the TM is open to all but some of the best stuff requires joining up.] 
Welcome.  And when you get around to it, being a full member costs something on the order of 10 cents a day; absolutely the best bargain I know of.   
Dennis DeNio
1968/69 280SL 004622, <100k, manual, 3.46, both tops, 670/904

280SL71

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Re: Mystery switch and dash lights
« Reply #5 on: January 23, 2013, 09:51:10 »
Can we see the picture of the switch or is it a secret?

Richard M, NYC
1969 280 SL, Tunis Beige, Euro Model (Italy).
Can be seen at www.panix.com/~rmadison/mercedes.shtml

Reischmann

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Re: Mystery switch and dash lights
« Reply #6 on: January 23, 2013, 12:40:47 »
Thanks Richard,
There is an attachment, with a picture of the switch plugged into the harness, just as I found it, at the bottom of my original email.
Best,
Mike

Reischmann

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Re: Mystery switch and dash lights
« Reply #7 on: January 23, 2013, 13:19:14 »
I beleive this momentary, normally open switch, is part of some other assembly. The dash lights work, with or without the switch in place.
I will continue to check the functionality of the other controls and let everyone know what I find.
Thank you,
Mike

w113dude

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Re: Mystery switch and dash lights
« Reply #8 on: January 23, 2013, 13:26:15 »
I beleive this momentary, normally open switch, is part of some other assembly. The dash lights work, with or without the switch in place.
I will continue to check the functionality of the other controls and let everyone know what I find.

Hi Mike,

If you follow the two wires from the micro-switch it's most probably going to the connector under the dash, then check to see which wires they are connected to from your wiring diagram. I'm curios to know what it is too.
Shaun Pooladian

67 250SL Auto late, Euro under restoration
70 280SE Coupe factory 5speed
72 250C  (for sale)
80 300CD, converted to 4sp manual, every day driver

georgem

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Re: Mystery switch and dash lights
« Reply #9 on: January 23, 2013, 19:50:00 »
Hmmm a puzzle allright.

Do your wind screen washers work - they use a momentary type switch. If the phantom switch, at one time could hang down below the dash, could it be a work round for a broken washer switch, or something in the engine start that needed a fix for starting?

If the switch was never  accessible, then it really is one of lifes mysteries.

Good hunting
George McDonald
Brisbane
230 Sl
1973 VW Kombi Single Cab Ute