The culprit is the alternator. Grit may become embedded under the alternator
brushes and it stops charging. This brings all the dash lights on
(that's one way to get your attention!). Or, the alternator is on its last
legs and will need new brushes or a complete rebuild.
I said I was going to get back to the group regarding all the warning lights in the dashboard of my 91 model standard 80 coming on. The final outcome is that the alternator is ok but there is also a square type plug that fits into the rear of the alternator. This plug on closer inspection had moisture and dirt inside it. I cleaned it and gave it a spray with some WD40. Also the lead from the battery that connects to the alternator with an "eyelet" connector via a 12mm nut was found to be rusty/corrosive nut. A clean with a piece of sand paper and hopefully I have fixed the problem .