6 Volt Coil Resistance

[tpenty1]

The new modern 6 volt coil from many vendors including NAPA do not identify (internal or external) resistance. How can I check which it is? I am having some trouble starting my 37 especially when it is hot. I wonder if this could be due to too much resistance (coil & resistance block under dash).

[Steves46]

With the modern coils, I'm 99.9% sure that they have internal resistors therefore that may explainn why you are having this problem. One way to check is to bypass your under dash resistor by using a jumper wire.

[bige386]

Do your self a favor and junk the modern style coil and get yourself an original 6volt coil and have it rebuilt by Skip Haney and rid yourself of that problem. I had the same problem with my 46 sedan. Bought one of Skips coils and have never had any problems starting my car sense.

[trainguy]

The NAPA coil I have bougth lately are marked that they have a internal risistor.Like bige said try Ships,you will not be sorry.I have had 2 Napa coil go south on me in the last 2 years.The condensers have been a problem also.Phil

[Old Henry]

Here's what the resistance should be:

[31chevy]

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I agree with bige386, His water pump rebuilds are also very good It sure helped my 34 Plus he is very nice to deal with.
Gary.

[Andy]

Old Henry, Are the resistances you show for a coil with or without the internal resister?
I have a coil supposidly without the resister and the car will not start hot. If I jumper the resister, it will shoot a spark 1/2 in long. Thanks

[Terry,OH]

tpenty1: For 6.V system with a 0.5 ohm auxiliary resistor, the coil primary should be in the range of 0.9 to 1.7 ohm. If the resistor is internal to the coil and you bypass the aux. resistor, the coil should be 1.3 to 2.2 ohm primary. If your using the 37 distributor with dual points, this will allow about 3 to 4.5 Amps to the coil circuit and through the distributor points, this should allow long point life since the one set of points fires the coil and has to break the current flowing in the coil circuit. I just measured one of Skips 37 coils it is 1.0 ohm

[rotorwrench]

The coil primary winding is wound internally in a similar fashion as a normal wire wound resistor is. They don't add a resistor inside of the modern coils, they just wind more wire into it to give it a higher resistance value internally. Round can type coils that are normally for 6-volt service don't need any extra windings. One that is designed for 12-volt service generaly is wound to work without an external ballast. The early 12-volt systems used a 6-volt coil and a ballast resistor to control the currnt going in there. The 12-volt service type coils didn't show up until after electronic ignitions became the norm.

[Old Henry]

Originally Posted by Andy

Old Henry, Are the resistances you show for a coil with or without the internal resister?
I have a coil supposidly without the resister and the car will not start hot. If I jumper the resister, it will shoot a spark 1/2 in long. Thanks

Those are without internal resistor.