Thanks everyone, the problem is solved!

I pulled the top engine cover off and discovered that the + cable from the battery was loose at the starter. I cleaned up the connector ends on the cables, snugged the 13mm nut down............. and no more flickering GEN light.
Now, on to the final polishing and prep to get the bike ready for sale.
Mark Fitzsimons
1982 R65
1984 R65
1981 R100RT