WD external ceramic terminal resistor

lpaz

Member
I had to replace the coil on my WD, and it had a ceramic external resistor block on that I ended up cracking and breaking. Does anyone know where I can obtain a replacement?
 
Ok Thanks!
I"ll check around, but the kids that work at the parts stores here are likely to just give me that "huh"? look on their face when I ask about it.
Didn"t know if there was a mail order place or a parts place may have known about.

Thanks for the replies!
 
The '57 Chevy used a "starting bypass" and the resistor was "fixed".

ASSUMING his Allis doesn't have a "starting bypass", a better choice would be a "ballast resistor", which LOOKS exactly the same, but it's resistance increases as it warms up. This makes for easier starting, then drops the voltage/current to the ignition system after startup for longer point life.

I have some info/part numbers I'll try to remember to post later.
 
Great!

Thanks. If I have some part numbers to go off of for the parts stores, that would definitely help.
 
coil primary resistance is governed by wire gauge and number of turns.. no resistos hide in there...
 
well, if you have a 12 volt coil on a 6 volt system, you can install a resistor to drop the voltage and make t he 12 volt coil do the job of a 6 volt coil.. RIGHT ??? If you dont think thats right, then what does the resistor do ? I was not trying to give an engineering explaination, just a simple black and white.
 
Your reasoning is backwards

There are 2 types of "12 volt" coils. One labeled "12 volts - external resistor required" (actually a 6 volt coil) and one labeled "12 volts no external resistor required". The first would work on a 6 volt system without an added resistor. the second would not.


A coil is a transformer with one leg of the primary and one leg of secondary tied together.

The difference in a "6 volt" coil and direct "12 volt" coil is in the number and ratio of the wire windings in the primary and secondary. The increased number of windings in primary of 12 volt coil increases the resistance. There is no separate resistor hidden in the can.

You can not use the "12 volt coil no external resistor required" in a 6 volt system. It's increased resistance will drop the current below the operating level. Adding a resistor will make it worse.

Your reasoning is backwards. The purpose of the resistor is to drop the 12 volt source to operate a 6 coil.

(do a search and study "Ohm's Law" and "Kettering ignition systems"
 
rvirgil laid it out for ya.

you can use a 6v coil with an extra resistro in a 12v system. but a 12v coil already has about twice the primary impeadance than a 6v coil and by itself would product a very weak spark if any at all on 6v. adding a resistor would make it worse and virtually no chance of any spark at all.. period.

as said. read up on ohms law. think about this. average 6v coil has a primary resistance of about 1-1.8 ohms average 12v coil has 3-3.5 ohms primary. that's why you can use a 6v on 12v with addition of a series resistor of appropriate value... but not the other way around...
 
OK, i see the problem now. Too much writing and not enough thinking. The original post does not say if he has a 12 volt or 6 volt system. If he had converted to 12 volt and still had the 6 volt coil, it would have a resistor to drop the voltage going into the old 6 volt coil. If he bought a new 6 coil he would still have the same problem. If he gets a new 12 volt coil and the tractor has been converted to 12 volts then no resistor is needed. I should have said the resistor makes the 12 volt BATTERY work with the 6 volt coil. Once you convert to 12 volts and have a 12 volt coil, the resistor is out of the picture.
 
no.. YOU DID

I replied to exactly what was typed.

you CANNOT add a resistor to a 12v coil and run it on a 6v battery :)

that's what was typed.
 
Again.. i replied to what was typed......

you CANNOT add a resistor to a 12v coil and run it on a 6v battery :)

that's what was typed. ;)
 
I guess thats my point. The original poster said he had a resistor. If you had spent the time trying to help him by saying... you probably have a 12 volt conversion and running an old 6 volt coil.... and now you may or may not need the resistor depending on the coil you bought, that would have been much help. I agree I posted wrong, saying coil instead of battery. Your post of how to install a 12 volt coil on a 6 volt system probaby was not much help either. I dont see anyone needing to do that.
 
Look.. i didn't reply to the OP... I replied to you.. because your advice about resistor and coil relationship to the OP was incorrect.

That was the limit of the scope of my reply....PERIOD.
 

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