Honda-SOHC

I can start my 400/4 up on the button ,but after about 3 to 5 mins it stops with total electrical failure. No lights, no neutral lights no horn. Leave it for about 5 mins hey presto it starts on the button. If I ride off it will fail again whereupon I wait at the side of the road for electricity to return and off I go . Not a very good way to travel !
Battery is in good condition . I have checked the obvious eg earthing, battery connections and wiring damage but nothing immediately obvious.
Any suggestions(polite!) as to where to look/ check next