I've been fighting a case of stobe lights on my 91 Explorer for over a year. At idle the lights would flicker and the voltmeter needle would swing back and forth like the voltage is fluctuating. I've cleaned connections, battery terminals, replaced the voltage regulator and nothing helped. A friend suggested it could be voltage being induced by the spark plug wires so I even changed them, too on the outside chance that he could be right! Two weeks ago, I noticed the positive battery cable was showing wear where the cable goes into the terminal connector, so I replaced both the positive and negative cables and the fluctuations have completely stopped in both the needle and the lights! Hope this helps and keeps someone from going thru what I went thru to fix this problem if it happens to them.
Ken