A Toyota distributor cap was part of the ignition system that was used for many years in the past. Today the Toyota engines no longer have points, condensers, or even a distributor to regulate the electrical impulse that is sent to the spark plugs. The distributor cap is located on top of a distributor that rotates along with the engine. The electrical impulse is directed to the contact posts inside the cap through the distributor rotor that is rotating on the shaft inside of the distributor. There is one connection for every cylinder in the Toyota engine. In the center of the Toyota distributor cap is where the ignition coil wire is connected to it. This is what provides the electrical current that will be directed to the different spark plugs by the distributor cap. It is the actual electrical current going through this ignition component that causes it to wear out over time. This is the same type of wear the spark plug electrodes experience over their life time. The contact surface of the distributor cap can be cleaned up leaving only a little amount of pitting and corrosion from the electrical current, but that reduces the size of the contact depth in which it makes contact with the distributor rotor. When this is done on your Toyota, the electrical current will not be able to flow when there is no longer direct contact between these two ignition components. During a tune up on the older vehicles not only should the distributor caps be replaced but also the distributor rotor, points, and condenser. All of these are ignition components that have now been replaced by the new style of electronic ignition systems on most modern vehicles.