In an internal combustion engine, the distributor cap serves to keep the wires in place between the electrodes of a distributor and the spark plugs.

It resembles the lid of a spray paint can, with one central hole on the top, and eight nodes circumscribing the the top, through which the wires pass.

"Down the line, coming down the line
A V6 Merc in blue
Without the sparks or distributor cap
I'll slap them on as it slides through"
-Moxy Früvous