I searched the internet. I found this: DISTRIBUTOR CAP AND ROTOR.—When problems point to possible distributor cap or rotor troubles, remove and inspect them. The distributor cap should be carefully checked to see that sparks have not been arcing from point to point. Both interior and exterior must be clean. The firing points should not be eroded, and the interior of the towers must be clean. The rotor tip, from which the high-tension spark jumps to each distributor cap terminal, should not be worn. It also should be checked for excessive burning, carbon trace, looseness, or other damage. Any wear or irregularity will result in excessive resistance to the high-tension spark. Make sure that the rotor fits snugly on the distributor shaft. A common problem arises when a CARBON TRACE (small line of carbonlike substance that conducts electricity) forms on the inside of the distributor cap or outer edge of the rotor. The carbon trace will short coil voltage to ground or to a wrong terminal lug in the distributor cap. A carbon trace will cause the spark plugs to either fire poorly or not at all. Using a droplight, check the inside of the distributor cap for cracks and carbon trace. Carbon trace is black which makes it hard to see on a black- colored distributor cap. If carbon trace or a crack is found, replace the distributor cap or rotor. There was a lot of trace onn the contact points. Cleaned this and all visible wireconnections in the engine compartment. No problems yet.