coil confusion

a friend told me on the old mopar ignition coils that with age can produce a weaker spark. i've only seen them work or not.can a old coil give a week spark?whats a stock voltage? thanks

I have had the oil leak out of them as they get old. And they will produce a weak almost orange spark and yet still work

Think of the coil as a step-up transformer..
Takes the 12V up to xx kv..
Inside it has many, many turns of enameled wire sitting in a round cylinder case with oil..
The oil bath is for cooling..

Over the years the enamel wire coating can degrade effectively shorting out some of its turns. This will reduce the coil's output voltage..