as herald is fitted with an non ballasted 12v system make sure the new coil has a 3 ohm primery, you may find the coil you have failing is from a ballasted system and is only 1.5 ohms, this ups the HT to blow things and consumes twice the current,so can melt points this may explain the extra heat, yes they get hot but not frying tonight. make sure the polarity is correct , what ever the battery earth is negative then the coil -ve goes to the dizzy, and +ve gets the white feed wrong way round will heat thing up and obscure misfires turn into failures, with little apparent to see why just some thoughts Peter