From one young man to two old gits, I have found that in my early days when I had a Crypton 321,an upside down secondary parade indicates that the coil was incorrectly reverse wired. This never caused the coil to over-heat though unless an incorrect coil was fitted. Just thought I would complicate things!
Regards
Pete M
PS. Never did really understand electrics anyway - cos you can't see it. Although I have felt it on the odd occaison