Posted: Thu Jul 12, 2012 8:45 am Post subject: Is a Number 504 coil internal ballasted?
Always a question, nothing goes without a hitch. Now that I got the old Auto-Lite IAD 4008 18D distributor off and got I new Omix-Ada distributor (electronic and pretty reasonable) the Omix-Ada intructions say the coil must be an internal ballasted coil or a in-line external ballast must be added to prevent damage to the electronic ignition. My coil has printed on it in various places Made in USA, 504, 97, 08 and 12V. I thought it might be a NAPA number - 504, but searching hasn't pulled anything up. Can anyone tell me if this is an internal ballasted coil? I don't want to add external ballast if it is ballasted, and I don't want to ask the parts guys a stupid question if I can get an answer here. _________________ 1952 M38
Joined: Nov 01, 2011 Posts: 201 Location: Escondido, CA
Posted: Thu Jul 12, 2012 2:59 pm Post subject:
I can't answer your exact question, but I found lots of discussions on old British car forums (mostly MGs) about coils and ballast resistors on 12V systems. Seems the way to differentiate is to measure the resistance across the primary side of the coil: 1.0 - 1.5 Ohm, external ballast resistor required; 3.0 Ohm, no ballast resistor needed. (The 3 Ohm is not really "internally ballasted", it just has more turns on the coil winding - more wire, more resistance.) Example discussion: http://www.britishcarforum.com/bcforum/ubbthreads.php/topics/608239/Pertronix_Flame_Thrower_Electr Hope this helps.
BTW, this should be in the Technical forum, not the For Sale forum. _________________ Jim McKim
1952 M38 son-father project
Slowly turning rusty parts into OD parts
Last edited by jimm on Thu Jul 12, 2012 3:01 pm; edited 1 time in total
Posted: Thu Jul 12, 2012 6:56 pm Post subject: I did check at the NAPA store
I found I was going past the NAPA store so I sucked it up, took the coil in - they didn't know much more then me. We think it is not ballasted because the crossover number goes to a NAPA coil that gives an external ballast number. Anyway they didn't have that external ballast nor an internal ballast coil - I elected to order the internal ballast coil - $56 or something street price, $36 my price. I will try the metering both of them tomorrow when I get the new one. And, no the old one doesn't have either internal ballast or non-ballast printed on it. _________________ 1952 M38
The coil issue is an ancient issue. Well discussed on all forums and a search of the forums will yield a lot of info both correct and incorrect.
This is an over simplification for this discussion.
The base line ignition energy needs from the 30's thru the 70's was met easily by the standard 6 volt coil. With the advent of 12 volt systems becoming increasingly popular in the mid 50's the auto electrical engineers saw no need to up the ignition system secondary output (those two score x 1000 voltage levels for sparking the fuel. The engines of the period had no need for any more secondary voltage so they stayed with the standard 6 volt coil. But to use that 6 volt coil they needed to drop the input voltage down to about 8 volts which is about where the 6 volt coil output peaked and would have been close to the cruise RPM generator outputs of the day So some manufacturers added an inline ballast resistor in the primary circuit between the coil and the ignition switch and others just added the increased internal primary resistance. Either way works just fine on your jeep. Essentially there is no difference between a 6 volt coil and a 12 volt coil that is maked for external resistance.
There is a significant advantage to using the external resistance system. You can run normal ignition switch to the coil voltage thru the ballast resistor so whenever the switch is in the run position you have about 8 volts entering the coil primary circuit. But if you have a key start starter you can run a ballast bypass wire from the starter solenoid's start signal post to the coils imput so a full 12 volt goes to the coil only while the starter is engaged. Makes for easier starts in the winter. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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