Great to hear that it was a quick find, and an easy fix !!
Rob Valdez has to get the credit for pinpointing this problem.
I wouldn't have thought about it, as my '81 uses a different grounding method, and is not prone to failure like the '79 and'80 year bikes.
It would still be a good idea, at some time in the future, to look over all of the electrical connections on the bike, I don't know how much corrosion could develop due to your normally damp conditions in the UK, I reside in a desert, and the bike rarely gets rained on, and gets washed twice a year whether it needs it or not, so corrosion is not an issue for me.
The side covers are known to break the 'spring' tab that goes over a rubber grommet, not much you can do to fix it, like Ed mentioned, small bungee cords, ty-wraps, or just leave them off, that's my current method.