Rheostat substitute

[awolff280sl]

Many of us have bypassed the nonfunctioning original rheostat which is NLA. Has anyone found an acceptable substitute that could be mounted, say, under the dash?
Also, at the risk of exposing my limited knowledge of electrical circuitry, I would think that a substitute rheostat could wire into the multipin connector in place of the bypass described by Al Lieffering.

[Cees Klumper]

Good idea - something for an aftermarket supplier in fact, since so many of these rheostats are now defective I would assume a working substitute in the same spot would see a lot of takers provided within the $15-$25 or so range.

[66andBlue]

I would rather repair the rheostat instead of mounting some contraption under the dash.
Many "dead" rheostats are really still functional after they have been carefully cleaned. Make sure you test them first before bypassing, it is really simple to do as described here: http://www.sl113.org/wiki/Electrical/Rheostat

[Cees Klumper]

Yes Alfred, that is even better ... My car came with the 'stat bypassed and I never tried to make it functional again. Will have to give it a try someday.

[awolff280sl]

Hi Alfred, years ago I tried to get my rheostat working but couldn't do it  and gave up and bypassed it. I think I remember the resistor coil was not in continuity, either broken or burned thru.
Anyway, I'm a sucker for contraptions (cruise control, central locking, intermittent wipers, etc,) as long as they are hidden, reliable, and reversible.
I am going to try out your LED suggestions, and thus a rheostat will be necessary given the brightness upgrade produced, from what I can see.
There are some generic "dashlight dimmers" out there so I'll give one a try. I'll post the results

[66andBlue]

Andy,
some time ago BarryD and I were looking for 12V DC rheostat replacements and thought that this company might have something useful: http://www.zane1.com/ and looked at these two: AD2-34L-12V and AMD-48R-12V.
We thought to put these in place of the original rheostat and not at a different location.
If you put a new one under thew dash you will have to feed wires into the center cluster because there is the first bulb that needs to be dimmed! 
Considering all the work required to substitute a new one I still believe that it is easier to fix the old one. What is so difficult soldering in a new coiled wire? 

[awolff280sl]

Alfred, thanks for not letting go of the repair option. Where does one find a new coiled wire?

Also, I don't understand why the under dash option would require feeding a wire to the center cluster as you say? Al Lieffering's rheostat bypass , performed at the “12 prong plug” on the metal bracket, results in illumination of all the dash lights, so I figure that all these lights could be dimmed with a rheostat there, instead of the jump he describes ("Shorting out the Rheostat" http://www.sl113.org/wiki/Electrical/Rheostat).

[Palolo]

Alfred, thanks for not letting go of the repair option. Where does one find a new coiled wire?

You might want to know what the resistance range is, that helps determine the gauge of wire to use.

Someone on BW wanted to repair a fuel level sender (vs pay $250+ for one) and I steered him to: http://www.resistancewire.com/mainpage.php?page=techinfo for some nichrome wire. They have many gauge sizes (wire diameter) to choose from.

The fuel level repair thread is here: http://www.benzworld.org/forums/vintage-mercedes-benz/1745985-how-fix-fuel-level-sender-w114.html

If you mess with it, post pics! 

[66andBlue]

Andy,
resistance wires are easily available, here is just one source: http://www.newportus.com/ppt/NIC60_80.html
It will require a more diligent search to find the one with the correct number of coils, length and resistance.

Also, I don't understand why the under dash option would require feeding a wire to the center cluster as you say? Al Lieffering's rheostat bypass , performed at the “12 prong plug” on the metal bracket, results in illumination of all the dash lights, so I figure that all these lights could be dimmed with a rheostat there, instead of the jump he describes

That is a very good question. I do not understand either why one needs to bypass the rheostat if the wire is broken. Why not move the rotating wiper all the way clockwise?  That creates a "short" between the gray/violet and the gray/blue wires the same way as Al's solution does.
Of course, if the wiper is defect, that is, not conductive any longer then Al's procedure is the easiest way to create a short.

Looking at the wiring diagram (see below) I can see that - rather than a jumper wire to create a bypass -  it might work putting a new rheostat between these two wires as you prefer.
Let us know when you succeed!  

[66andBlue]

You might want to know what the resistance range is, that helps determine the gauge of wire to use.
.......
If you mess with it, post pics! 

Patrick,
you beat me to the punch!
The resistance is about 18 Ohms across the full length. Now one would need to know the coil diameter and the number of turns to calculate the correct thickness (gauge).

[Palolo]

Patrick,
you beat me to the punch!

Sorry! However, I do prefer sangria. Have all the punch you want... 

[al_lieffring]

The internal working components in the rheostat are interchangeable with the more common 108,114,115 models, The outside ceramic housing is not adaptable, but it can be taken apart and the innards salvaged and used for replacement parts.