I have yet to see anyone say anything about checking/cleaning the ground connections.
Being an old VW guy, we've learned to check that first. Germans love to put ground connections everywhere, so that means the possibilities of figuring out WHICH ground was bad, was like a treasure hunt. Check and clean your grounds. Also, I've noticed that these older cars love to smoke a little at the ignition switch. They are over 20 years old and electronics tend to fail sooner or later.
Sure hope this helps.