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Clum Headlight Switch Dimming Coil


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Hello everyone,


Is there a modern coil or resistor used to replace the dimming coil used on Clum headlight switches? I have a 1926 Dodge Brothers with the 6 volt 2 unit system. 


Like the coil seen in this photo:




Photo courtesy of R.White 

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1 hour ago, TonyAus said:

Check the impedance (resistance) of the old coil with a multimeter . I have a vague recollection that it should be in the area of one ohm.

I will check.  


Do you know what disadvantages there are to using the original? I only assume it wouldn’t be a good idea  since it’s essentially just a coil of wire that I assume could cause a fire. 

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I tried measuring the resistance of my old coil and my readings were strange. The number kept jumping around depending on where I took the measurement on the ring terminals. I was getting .80 kOhms, 100 kOHms and .1 kOhms at different times. I probably need to clean the terminals really well. 


I went ahead and tested the coil in a circuit using my battery eliminator. I had the coil in series with a 6 volt bulb. It dimmed it down pretty far, just had a warm glow. And boy did it get hot. 


By the way, is that asbestos covering the wire? It sure reminds me of asbestos. 



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17 minutes ago, nearchoclatetown said:

DB26, I think you are thinking too much. DB headlights were only 32 candlepower. Does it really matter if the low beam is 26 or 16?

You have a point. But any comments on the asbestos and it getting really hot? 

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It is going to get hot. I don't see any asbestos, I wouldn't want any today either.


A resistance of the original value will dissipate the same amount of heat when used with the same bulbs, period. You could use a modern resistor, Something much larger would reduce the surface temperature, even though the total amount of heat released would be the same. Then you would probably have to support the resistor, and do so with something that would not catch fire.


I just looked again and I still don't see asbestos. If this were a tube around the outside of the coil, perhaps you could use some of the fiberglass woven tubing used as high temperature insulation in appliances.


If the bulbs were of a different candlepower (that would imply a different wattage), the resistance of the coil would have to change also to get similar dimming results.


Assuming this resistor dims both bulbs, you need the correct wattage bulbs, both in the circuit, wired as they are in the car, for any sort of meaningful test.


Edited by Bloo (see edit history)
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I am not positive what you are trying to achieve here, but try this. Take a ballast resistor and hook it to your switch. A ballast resistor was used by Chrysler Products well into the 70's to lower voltage to the ignition points. Should be easy to find even new if you have to. It has a bracket to hold it, and porcelain to insulate it, but ti's still going to get hot. 

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Wow thanks for all the replies everyone! 


First off, I know using the dimming coil would be something I don’t do often, but I wanted to add it back in for originality. I just love putting things back to the way they were from the factory. I can show it off to someone somewhere at some car show and note how dim the lights are and then note how dim they are with the dimmer added in. 


Second, the picture I used it not my actual switch and coil, it was borrowed from @R.White


This is my coil:




I was concerned about the fuzzy exterior being asbestos. 


I know resistors get hot, I was just fishing for any warning from members with much more experience than me. I can clearly see that my questions are a bit over cautious, so I will shed my doubts and run the coil in the car. 

Edited by DB26 (see edit history)
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