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Wes, I have two used coils. On both, the primary resistance is 12.5 ohms.
The secondary resistance is 10.10K and 10.15K ohms.

Referencing to your photo of the coil on a previous post shows primary resistance of 5 to 6.2 ohms. And secondary 9k to 12k.

My coils secondary resistance are in the tolerance range of your test. But the primary is twice as high as yours.

Could I take it that these coils are bad? Its peculiar that both of the coils measure practically the same.

Ken

Ken,
What do your primaries ohm at when hot?

I don't know Wes. I got the coils during my restoration and kept them for spares.

Is it ok to apply 24 volts to them for a short period maybe 15 to 20 seconds and check the resistance? Or best to put them in the distributor and run them assuming they are good to run.

You just heat the coils with a hair dryer or heat gun until they just start to get uncomfortable to touch or hold. Then measure their resistance.

I have a spare 24 volt coil, i will measure the resistance this evening, i let you know.

Erik

I checked the coil, i have two M151 coils also 24 volt and same dimensions.

primary 12,8 ohm

secondary 12k ohm

cold measured on a spare one ( same as in use on my38 )

as info :
i use a mutt m151 coil in my distributor together with the swiss solid state ignition all on 24 volt

I heated up the coils and the restistance only changed 3/10ths of an ohm.
Maybe different manufactures had different turns ratios in their coils

Ken

Does anyone know what amount of change of resistance on the primary and secondary windings from cold to hot indicates that the coil is not good?