72 318...need voltage number into coil please

i'm posting this for a friend of mine with a 72 challenger with a 318...

72 challenger 318 stock electronics, i'm getting 12.5v at the battery, getting 12.5 from battery ground to the fuse box under the steering wheel, once key is turned to ignition (not starting, but on) all voltage drops to 10.2v. i'm trying to figure out if 10.2v is normal going into the coil or should i be getting the full 12.5v? and yes, i replaced the external ballast. i want to make sure i dont fry the coil.

thanks guys

The ballast resistor drops the voltage so you are in the ballpark. The ballast is bypassed in the start positon so the coil gets full 12v while cranking.

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The ballast resistor drops the voltage so you are in the ballpark. The ballast is bypassed in the start positon so the coil gets full 12v while cranking.

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thanks a lot stumpy! i'll let him know!