you won't be able to return a used ignition coil.

i think the stock coils are 3 ohms.
to measure- just put your voltmeter leads across the + and - terminals.

what electronic ignition have you purchased?

i'm sure someone will correct me if i'm talking out of my rear here, but-
i imagine that the the directions from the ignition mean your coil must have *at least* 1.5 ohms of primary resistance.